<PAGE>   1

                                                                     Exhibit 9.1

                                     AMENDED
                      VOTING TRUST AGREEMENT IN RESPECT OF
                  COMMON STOCK OF DIGITAL POWER HOLDING COMPANY

         This Voting Trust Agreement (the "Agreement") effective as of May 6,
1998, and as now amended between I-Storm Acquisition Corp., a Cayman Islands
company and an owner and holder of shares of the Common Stock (the "Holder") of
Digital Power Holding Company (the "Corporation"), a corporation organized and
existing under the laws of the State of Nevada; and the Secretary of the
Corporation (the "Trustee").

         WHEREAS, the Holder entered into a Stock Purchase Agreement on May 6,
1998 herewith pursuant to which the Holder acquired sixty (60) percent of the
issued and outstanding Common Stock of the Corporation;

         WHEREAS, as condition of the Stock Purchase Agreement, the Holder must
vest its voting power of its Common Stock of the Corporation, including any
Common Stock acquired through the exercise of options granted to it by the Stock
Purchase Agreement, in the Trustee as hereinafter provided;

         WHEREAS, with a view to the safe and competent management of the
Corporation in the interests of all the shareholders thereof, and in the
interest of preventing the Holders from exercising direct or indirect control
over the management and fundamental decisionmaking of the Corporation, the
subscribers are desirous of creating a trust in the manner following;

         NOW, THEREFORE, for and in consideration of the mutual promises and
covenants set forth herein, the receipt and sufficiency of which is hereby
acknowledged, it is mutually agreed as follows:

         1.       TRANSFER OF STOCK TO TRUSTEE. The Stockholder shall deposit
with the Trustee the certificate or certificates representing its Common Stock
of the Corporation, together with a proper and sufficient instrument, duly
executed, for the transfer to the Trustee, and with all necessary transfer tax
stamps affixed. Shares of Common Stock of the Corporation received by the
Stockholder through the exercise of options granted to it pursuant to the Stock
Purchase Agreement shall immediately be deposited with the Trustee at the time
of exercise and such shares and options shall be governed by and subject to this
Voting Trust Agreement.

         2.       VOTING TRUST CERTIFICATES.

                  (a) Upon deposit of a certificate or certificates representing
Common Stock of the Corporation by the Stockholder, the Trustee shall deliver or
cause to be delivered to the Holder, a voting trust certificate or certificates
for the same number of shares of Common Stock of the Corporation as is
represented by the certificate or certificates so deposited, which voting trust
certificate or certificates so to be delivered shall be substantially in the
form attached hereto as Exhibit A with such amendments and modifications as
shall be approved by the Trustee. A copy of this Agreement shall be filed by the
Trustee in the principal office of the Corporation.

<PAGE>   2

                  (b) The voting trust certificates issued by the Trustee may
only be transferred on the books of the Trustee upon the surrender of any and
all voting trust certificates, properly endorsed by the Holder. Any transfer of
the voting trust certificates shall be subject to the same restrictions
governing the transfer of the underlying Common Stock of the Corporation imposed
by the Corporation, including those imposed by the provisions of any shareholder
agreement, or any federal or state law or regulation. Until such transfer, the
Trustee may treat the Holder as owner of the voting trust certificate for all
purposes whatsoever. In connection with any transfer of such voting trust
certificates under any provision of this Agreement, the Trustee may require the
payment of a sum sufficient to pay or reimburse him for any resulting stamp tax
or other governmental charge. Except in the case of a transfer made in a bona
fide sale for value to an unrelated third party, every transferee of a voting
trust certificate or certificates issued shall, by the acceptance of the voting
trust certificate or certificates, become a party to this Agreement with like
effect as though an original party, and shall be considered a Holder.

                  (c) Shares of Common Stock of the Corporation, certificates
for which shall be deposited with the Trustee, shall be vested in the Trustee
and shall be transferred into the name of the Trustee upon the books of the
Corporation. The Trustee shall, as to all Common Stock so held by him, possess
and be entitled to exercise all shareholders' rights of every kind, including
the right to vote and take part in, or consent to, any corporate or
shareholders' action, in accordance with the terms of this Agreement.

         3.       HOLDERS SHALL NOT VOTE. Each Holder shall not have any right,
with respect to any such Common Stock held by the Trustee, to vote, or take part
in or consent to, any corporate or shareholders' action of the Corporation.
Holder acknowledges it has acquired the shares and options of the Corporation as
a passive investment and not to control the management of the Corporation. Each
Holder assumes no responsibility for the acts of the Trustee, or of any director
elected in the exercise of the voting power of the Common Stock.

         4.       TRUSTEE TO VOTE STOCK. The Voting Trustee shall vote on
matters which may come before him at any shareholders' meeting and agrees to
vote the Common Stock held by it pursuant hereto in the same manner as the
majority of the shares of Common Stock which are not subject to this Voting
Trust are voted; and further, in the event that a majority of the shares of
Common Stock which are not subject to this Voting Trust should take action by
written consent in lieu of a meeting or stockholder vote, the Trustee shall
immediately thereafter take action by written consent in the same manner as the
majority of the shares of Common Stock which are not subject to the Voting Trust
have taken such action. The Trustee shall have no obligation to give advance
notice to any Holder of any pending vote or corporate action. The Trustee shall,
however give notice to the Holders of any shareholder action, including his
exercise of voting power, within ten (10) days after the occurrence of such
action.

         5.       APPOINTMENT OF TRUSTEE TO FILL VACANCIES.

                  (a) In the event of a vacancy, by resignation or otherwise, in
the role of Trustee, the Holders shall, at a special meeting, appoint by a vote
of the Holders of a majority of the shares of Common Stock held in the Voting
Trust at that time, appoint a successor to the vacancy. Any such successor shall
sign an agreement to be bound by this Agreement, and to perform the terms
thereof, as if such successor had originally signed this Agreement. The
selection of a Trustee shall be limited to such entities or individuals which
are unrelated third parties to any


                                       2
<PAGE>   3

Holder. No Holder, or any individual or entity directly or indirectly controlled
by a Holder, or in which a Holder has any financial, contractual, beneficial, or
voting relationship or interest, shall serve as a Trustee under this Voting
Trust Agreement.

          (b) The Holders of a majority of the shares of Common Stock of the
Corporation at the time held in the Trust may, at any time, determine to remove
a Voting Trustee, by signing a resolution to such effect and filing it with the
Secretary of the Corporation. The successor to such Trustee shall be appointed
in accordance with Section 5(a) hereof.

         6.       DIVIDENDS. Each Holder shall be entitled, until distribution
of Common Stock in the Corporation, as provided for herein, to receive, from
time to time, payments equal to the dividends, if any, other than such as shall
be in the form of shares of Common Stock of the Corporation, collected by the
Trustee upon the like number of shares of Common Stock of the Corporation as is
specified in the voting trust certificate. Payments are to be mailed to the
Holders of the voting trust certificates entitled to receive the dividends, at
their addresses as filed with the Trustee. In the event that any dividends paid
in Common Stock of the company shall be received by the Trustee, the respective
holders of voting trust certificates issued under this Agreement shall be
entitled to the delivery of new or additional voting trust certificates to the
amount of the Common Stock received by the Trustee as such dividend upon the
number of such shares of the company represented by their respective voting
trust certificates previously outstanding. The record date for determining the
Holders entitled to any payment or distribution of dividends shall be the same
record date fixed pursuant to the Bylaws of the Corporation for the
determination of the Common Stockholders entitled to receive such payment or
distribution, and only the Holders of record on that date shall be entitled to
participate in such payment and distributions.

         7.       SUBSCRIPTION OF ADDITIONAL COMMON STOCK. If any Common Stock
or other securities of the Corporation are offered for subscription to the
holders of the Common Stock deposited hereunder, the Trustee, promptly upon
receipt of notice of such offer, shall deliver a copy of such notice to each
holder of a voting trust certificate. Upon receipt by the Trustee of a request
from any Holder of a voting trust certificate to subscribe in his behalf,
accompanied with the sum of money or other consideration required to pay for
such Common Stock or securities (not in excess of the amount subject to
subscription in respect of the shares represented by the voting trust
certificate held by such holder), the Trustee shall make such subscription and
payment. Upon receiving from the Corporation the certificate for shares or
securities so subscribed for, the Trustee shall issue to such Holder a voting
trust certificate in respect if the shares or securities received have general
voting powers. If, however, the shares or securities do not have voting powers,
the Trustee shall mail or deliver such securities to the Holder in whose behalf
the subscription was made, or may instruct the Corporation to make delivery
directly to the certificate holder entitled thereto.

         8.       MERGER OR CONSOLIDATION. If the Corporation is merged into or
consolidated with another corporation, or all or substantially all of the assets
of the Corporation are transferred to another corporation, then in connection
with any of the foregoing, the term "Corporation" for all purposes of this
Agreement shall be deemed to include such successor corporation, and the Trustee
shall receive and hold under this Agreement any Common Stock of such successor
corporation received on account of the ownership, as the Trustee hereunder, of
the Common Stock held hereunder prior to such merger, consolidation and
transfer. Voting trust certificates issued and outstanding under this Agreement
at the time of such merger, consolidation or transfer may remain outstanding or
the Trustee may, in his discretion, substitute for the voting trust certificates
new


                                       3
<PAGE>   4

voting trust certificates in appropriate form, and the term "Common Stock"
shall include any capital Common Stock which may be received by the Trustee in
lieu of all or any part of the Common Stock of the Corporation.

         9.       ACTION WITHOUT MEETING. Any action required or permitted to be
taken at any meeting of the Holders may be taken without a meeting if a written
consent or consents to such action is signed by all Holders and delivered to the
Trustee. Notice of any meeting to be held pursuant hereto shall be given in the
manner provided in the Bylaws of the Corporation relative to notice and purpose
of Common Stockholders' meetings and shall be held and conducted in accordance
with the Bylaws of the Corporation relative to Common Stockholder's meetings.

         10.      AMENDMENT OF VOTING TRUST. If at any time the Trustee shall
deem it advisable to amend this Agreement, the Trustee shall submit such
amendment to the Holders for a majority approval at a meeting called for that
purpose. If at any time any of the Holders shall deem it advisable to amend the
Agreement, such Holder shall submit such amendment to the Holders for a majority
approval at a meeting called for that purpose.

         11.      TRUSTEE ACCEPTANCE. The Trustee accepts the trusts under this
Agreement subject to all the terms, conditions and reservations herein
contained, and agrees that he will exercise the powers and perform the duties of
Trustee as set forth; provided, however, that nothing herein contained shall be
construed to prevent any or all Trustees from resigning and discharging
themselves from the trust.

         12.      TERMINATION.

                  (a) This Agreement and the Trust hereby created shall be
continued until May 6, 2003, and then automatically shall terminate; provided,
that the duration of this Agreement and the Trust may be extended upon consent
of the Holder for a period not to exceed an additional fifteen years, as set
forth in Section 78.365 of the Nevada Revised Statutes, except that such
Agreement shall be terminated with respect to the shares of Common Stock which
are represented by the Voting Trust Certificate of any Holder upon a transfer of
such Common Stock for value in a bona fide sale for value to an unrelated third
party; or in the event that the aggregate number of such shares of Common Stock
which are represented by the Voting Trust Certificates held collectively by the
Holders hereunder at any time shall represent less than ten (10) percent of the
total number of shares of outstanding and issued voting Common Stock of the
Corporation, this Agreement and the Trust shall be automatically terminated.

                  (b) At any time after the termination of this Agreement, the
Holders shall, upon surrender for cancellation of their voting trust
certificates and upon payment of any transfer tax required by law, be entitled
to receive certificates for the number of shares of Common Stock represented by
their respective voting trust certificates.

         13.      NOTICE. Any notices to be provided to the Holder or to the
Trustee pursuant to this Agreement shall be provided to each, respectively, as
set forth in Attachment B hereto. The Trustee, further, shall advise the Holders
in writing within three days receipt of notice of any shareholder vote, and
further, shall provide prompt notice to the Holder of any action taken by the
Trustee pursuant to this Agreement.

                                       4
<PAGE>   5

         14.      GOVERNING LAW. This Agreement and the voting trust created
hereby shall be governed for all purposes by the laws of the State of Nevada.

         All voting trust certificates issued by the Trustee hereunder shall
have enclosed thereon a statement that they are held in accordance with and
subject to the terms of this Voting Trust Agreement.

         IN WITNESS WHEREOF, the parties hereto have executed this Voting Trust
Agreement.

                                    VOTING TRUSTEE:

                                    -------------------------------------------

                                    By:
                                        ----------------------
                                    Date:
                                          -------------------------------------

                                    HOLDER:

                                    I-STORM ACQUISITION CORP.

                                    By:
                                         --------------------------------------
                                         Name:
                                         Title:

                                       5
<PAGE>   6


                                    EXHIBIT A

THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER
THE SECURITIES ACT OF 1933, AS AMENDED, OR UNDER APPLICABLE STATE LAW, AND MAY
NOT BE SOLD, TRANSFERRED, PLEDGED, HYPOTHECATED OR OTHERWISE DISPOSED OF IN THE
ABSENCE OF (i) AN EFFECTIVE REGISTRATION STATEMENT FOR SUCH SECURITIES UNDER
SAID LAWS OR (ii) AN EXEMPTION THEREFROM UNDER SAID LAWS.

                            VOTING TRUST CERTIFICATE
              FOR SHARES OF STOCK OF DIGITAL POWER HOLDING COMPANY

Certificate No. 001                               600,000 Shares of Common Stock



         This is to certify that I-Storm Acquisition Corp. has deposited under
the Voting Trust Agreement dated as of May 6, 1998 (the "Voting Trust
Agreement"), between the owners and holders of certain shares of the Common
Stock of Digital Power Holding Company, a Nevada corporation (the
"Corporation"), and _____________ (the "Trustee"), a certificate or certificates
for 600,000 shares of Common Stock of the Corporation.

         Until the termination of the Voting Trust Agreement, the holder of this
voting trust certificate (the "Holder") is entitled to receive payments equal to
the amount of dividends, if any, other than such as shall be in the form of
shares of Common Stock of the Corporation, received by the Trustee on the shares
of Common Stock represented by this certificate, less any taxes imposed which
the Trustee may be required to pay, and also less a proportionate share of the
expenses of the Trustee. In the event that any dividends paid in Common Stock of
the Corporation shall be received by the Trustee, the respective holders of
voting trust certificates issued under this Agreement shall be entitled to the
delivery of new or additional voting trust certificates representing the amount
of the Common Stock received by the Trustee as such dividend.

         Upon the termination of the Voting Trust Agreement, the Holder shall be
entitled to receive a Common Stock certificate or certificates for the number of
shares of Common Stock represented by this certificate. Until actual delivery to
the Holder of such Common Stock certificate or certificates, the Trustee shall
be entitled to exercise all rights and powers of absolute owners of record of
the Common Stock deposited, including the right to vote and to consent to or
waive any act of the Corporation of any kind.

         A duplicate original of the Voting Trust Agreement has been filed in
the principal place of business of the Corporation and shall be open to
inspection, during business hours, by any shareholder of the Corporation or his
attorney.

         At any time after the termination, the Holders will be entitled, upon
surrender for cancellation of their respective voting trust certificate(s) and
upon payment of the transfer tax required by law, to receive certificates for
the number of shares of Common Stock represented by


                                       6
<PAGE>   7

their respective voting trust certificates. Stock certificates shall be
delivered by the Trustee to the Holder.

         In the event of the dissolution or total or partial liquidation of the
Corporation, any proceeds received by the Trustee for the Common Stock
represented by this certificate shall be delivered to the Holder of record, but
only upon surrender of this certificate in the case of a dissolution, or the
presentation of this certificate for a notation in the case of a distribution in
a partial liquidation.

         This voting trust certificate and the right, title and interest in and
to the shares of Common Stock for which this voting trust certificate is issued,
are transferable on the books of the Trustee by the registered Holder. And,
until transferred, the Trustee may treat the registered Holder as the owner for
all purposes whatsoever except that no delivery of Common Stock certificates
shall be made without the surrender of this voting trust certificate.

         As a condition of permitting any transfer or delivery of Common Stock
certificates or voting trust certificates, the Trustee may require the payment
of a sufficient sum to reimburse it for any stamp tax or other governmental
charge in connection with such transfer and for a proportionate part of its
expenses as Trustee.

         IN WITNESS WHEREOF, the Trustee has caused this voting trust
certificate to be signed effective as of the 6th day of May, 1998.


                                      VOTING TRUSTEE:

                                      -----------------------------------------

                                      By:
                                          --------------------------------------

                                      Name:
                                            -----------------------------------
                                            Secretary


                                       7
<PAGE>   8

To Be Completed Upon Transfer:



         FOR VALUE RECEIVED, __________________________________ hereby sells,
assigns and transfers to ____________________________, the within certificate
and all rights and interests represented, and does hereby irrevocably appoint
________________________________ Attorney to transfer the same on the books of
the Trustee, with full power of substitution in the premises.

Dated:
       --------------------

                                      -----------------------------------------

In the presence of:

---------------------------


                                       8