<PAGE>

                                                                  Exhibit 10(xi)

                                        THIRD 
                                 AMENDMENT AGREEMENT

    This AMENDMENT AGREEMENT, dated as of the 14th day of December, 1995 (this
Amendment") is by and among INVERNESS CORPORATION, with a principal place of
business at Mill Crossing, Kensington, Connecticut ("Lender"), and POWER
DESIGNS, INC., a New York corporation with a principal place of business at 250
Executive Drive, Edgewood, New York ("Borrower").

    On January 16, 1995, Lender made a $200,000.00 revolving credit loan (the
"Loan") to Borrower. The Loan was made pursuant to a Revolving Loan Agreement
(as amended and in effect from time to time, the "Loan Agreement"), dated
January 16. 1995, is evidenced by a Commercial Promissory Note in the original
principal amount of $100,000 (as amended and in effect from time to time the
"Note") dated January 16, 1995 and is secured pursuant to a Security Agreement
(as amended and in effect from time to time, the "Security Agreement") dated
January 16, 1995.

    Borrower has requested that Lender amend the Loan Agreement in order to (i)
increase the maximum principal amount of the Loan, (ii) make other related
changes. Lender has advised Borrower that Lender is prepared to make the
amendments requested on the condition that Borrower join with Lender in this
Amendment.

    In consideration of this Amendment and for other good and valuable
consideration, the receipt and sufficiency of which is hereby acknowledged,
Lender and Borrower hereby agree as follows:

    1.   DEFINITIONS. Capitalized terms used herein shall have the meanings
given to them in the Loan Agreement.

    2.   AMENDMENT TO SECTION 1.1 OF THE LOAN AGREEMENT. Section 1.1 of the
Loan Agreement is hereby deleted in its entirety and in lieu thereof the
following is substituted:

    " 1.1 The Line of Credit. Pursuant to the terms of this Agreement and upon
satisfaction of the conditions precedent referred to in Section 3 hereof, the
Lender may, in its sole discretion, lend to Borrower, and the Borrower may, in
its sole discretion, borrow from Lender, advances not to exceed the principal
amount of THREE HUNDRED THOUSAND AND 00/100 DOLLARS ($300,000) (the "Line of
Credit") during the period from the date hereof to March 29, 1996 (the
"Termination Date") as evidenced by a promissory note (the "Note") in
substantially the form of Exhibit 1 hereto. Advances shall be made in such
amounts as the Lender, in its sole discretion, shall determine; however, in no
event shall the sum of any advance and the outstanding principal balance of the
loan be less than TEN THOUSAND ONE HUNDRED DOLLARS ($10,100)"

3.  AMENDMENT TO EXHIBIT L OF THE LOAN AGREEMENT. Exhibit 1 of the Loan
Agreement is hereby amended in the same manner as set forth in Section 4. Below.

                                         A-1

<PAGE>

4.  AMENDMENT TO NOTE. The Revolving Credit Note, as amended, is hereby amended
(i) by deleting therefrom the words "$200,000.00" wherever they appear and
inserting in lieu thereof the words "$300,000.00", (ii) by deleting therefrom
the words "TWO HUNDRED THOUSAND" wherever they appear and inserting in lieu
thereof the words "THREE HUNDRED THOUSAND".

    5.   RATIFICATIONS. ETC. Except as otherwise expressly set forth herein all
terms and conditions of the Loan Agreement, Note and the Security Agreement are
ratified and shall remain in full force and effect. Nothing herein shall be
construed to be a waiver of any requirements of Loan Agreement, the Note and the
Security Agreement except as expressly set forth herein. The Guarantors hereby
ratify and confirm their respective obligations under their respective
guaranties with respect to the Note as amended hereby.

    6.   CONDITIONS TO EFFECTIVENESS. This Amendment shall be effective upon
its receipt by Lender, duly executed by Borrower.

    7.   COUNTERPARTS. This Amendment may be executed in any number of
counterparts, coach of which shall constitute an original and all of which
together shall constitute one instrument.

    8.   GOVERNING LAW. This Amendment shall be construed and interpreted in
accordance with the laws of the State of Connecticut

    IN WITNESS WHEREOF, the parties hereto have executed this Amendment on the
date first written above.


                                       LENDER: 
                                       INVERNESS CORPORATION 


                                       By                                 
                                         ---------------------------------
                                            Its 
                                            Duly Authorized

                                       BORROWER: 
                                       POWER DESIGNS, INC.


                                       By   /s/ Melvin Becker             
                                         ---------------------------------
                                            Its President 
                                            Duly Authorized 

                                         A-2