EX-4.3



 Exhibit 4.3 

SECOND SUPPLEMENTAL INDENTURE 
 TO
BE DELIVERED IN CONNECTION WITH THE VISTRA ACQUISITION 
 SECOND SUPPLEMENTAL INDENTURE (this “Supplemental Indenture”), dated as
of April 9, 2018, between Vistra Energy Corp., a Delaware corporation (the “Successor”), and Wilmington Trust, National Association, as trustee under the indenture referred to below (the “Trustee”). Unless otherwise defined
in this Supplemental Indenture, capitalized terms used herein without definition shall have the meanings assigned to them in the Indenture (as defined below) and the Purchase Contract Agreement (as defined below). 

WITNESSETH 
 WHEREAS, Dynegy Inc.
(“Dynegy”) has outstanding 4,600,000 Tangible Equity Units, each consisting of (i) a prepaid stock purchase contract (each, a “Purchase Contract”) pursuant to which the holder thereof shall have the right from time to time
to receive a number of shares of common stock of Dynegy determined pursuant to the terms of the Purchase Contract and the Purchase Contract Agreement, dated as of June 21, 2016 (the “Purchase Contract Agreement”), among Dynegy and
Wilmington Trust, National Association, as purchase contract agent, and as Trustee, pursuant to which the Units and the Purchase Contracts were issued and (ii) a 7.00% Senior Amortizing Note due 2019 (collectively, the “2019 Amortizing
Notes”), $87,165,860 aggregate principal amount of which were initially issued under that certain Indenture, dated as of June 21, 2016 (the “Base Indenture”), by and between Dynegy and the Trustee, as supplemented by the First
Supplemental Indenture, dated as of June 21, 2016 (the “First Supplemental Indenture” and, together with the Base Indenture, the “Indenture”), by and between Dynegy and the Trustee; 

WHEREAS, the Successor has filed with the Secretary of State of the State of Delaware a Certificate of Merger, dated as of April 9, 2018,
which provides for the merger of Dynegy with and into the Successor (the “Merger”), with the Successor continuing its corporate existence under the laws of the State of Delaware as the surviving company of the Merger; 

WHEREAS, as a result of the Merger, the Successor shall assume the obligations of Dynegy under the Units, including, for the avoidance of
doubt, with respect to the Purchase Contracts and the 2019 Amortizing Notes; 
 WHEREAS, Section 7.01 of the First Supplemental
Indenture provides, among other things, that Dynegy may consolidate or merge with or into another Person or sell, assign, transfer, lease or otherwise dispose of all or substantially all of the properties and assets of Dynegy and its Subsidiaries
taken as a whole to another Person; provided that, among other things, the Person formed by or surviving any such consolidation or merger (if other than Dynegy) or the Person to which such sale, assignment, transfer, conveyance or other
disposition has been made assumes all the obligations of Dynegy under the 2019 Amortizing Notes and the Indenture pursuant to a supplemental indenture; 

WHEREAS, Section 8.01 of the First Supplemental Indenture provides, among other things, that the Indenture (with respect to the 2019
Amortizing Notes) or the 2019 Amortizing Notes (whether or not part of a Unit) may be amended or supplemented without the consent of 

  
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any Holder of the 2019 Amortizing Notes to evidence the succession by a successor corporation and to provide for the assumption by a successor of Dynegy’s obligations under the Indenture;
and 
 WHEREAS, the Successor desires and has requested that the Trustee join in the execution of this Supplemental Indenture for the
purpose of evidencing such assumption by the Successor. 
 NOW THEREFORE, in consideration of the foregoing and for good and valuable
consideration, the receipt of which is hereby acknowledged, the Trustee and the Successor mutually covenant and agree for the equal and ratable benefit of the Holders of the 2019 Amortizing Notes as follows: 

ARTICLE 1 
 ASSUMPTION AND
AGREEMENTS 
 Section 1.1. The Successor hereby, in accordance with the terms and conditions of the Indenture,
assumes the due and punctual payment of the principal of, premium, if any, Additional Interest, if any, and interest on the 2019 Amortizing Notes, and the due and punctual performance and observance of all other covenants, conditions and other
obligations contained in the Indenture and the 2019 Amortizing Notes on the part of Dynegy to be performed or observed. 

Section 1.2. The Successor shall succeed to, and be substituted for, and may exercise every right and power of,
Dynegy under the Indenture and the 2019 Amortizing Notes with the same effect as if the Successor had been named as “the Company” therein. 

ARTICLE 2 
 MISCELLANEOUS 

Section 2.1. NEW YORK LAW TO GOVERN. THE INDENTURE, THIS SUPPLEMENTAL INDENTURE AND THE 2019 AMORTIZING NOTES SHALL
BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK. 
 Section 2.2. Counterparts.
The parties may sign any number of copies of this Supplemental Indenture. Each signed copy shall be an original, but all of them together represent the same agreement. 

Section 2.3. Effect of Headings. The Section headings herein are for convenience only and shall not affect the
construction hereof. 
 Section 2.4. The Trustee. The Trustee shall not be responsible in any manner whatsoever
for or in respect of the validity or sufficiency of this Supplemental Indenture or for or in respect of the recitals contained herein, all of which recitals are made solely by the Successor. 

  
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 Section 2.5. Ratification of Indenture; Supplemental Indenture Part of
Indenture. Except as expressly amended hereby, the Indenture is in all respects ratified and confirmed and all the terms, conditions and provisions thereof shall remain in full force and effect. This Supplemental Indenture shall form a part of the
Indenture for all purposes, and every Holder of the 2019 Amortizing Notes heretofore or hereafter authenticated and delivered shall be bound hereby. 

[Signature pages follow] 

  
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 IN WITNESS WHEREOF, the parties hereto have caused this Supplemental Indenture to be duly
executed and attested, all as of the date first above written. 
  

					
	 VISTRA ENERGY CORP.,
 as
Successor

		
	By:	 	 /s/ Kristopher E. Moldovan

	Name:	 	Kristopher E. Moldovan
	Title:	 	Senior Vice President and Treasurer


 [Signature Page to 7.00% Amortizing Notes Supplemental Indenture] 







 
					
	 WILMINGTON TRUST, NATIONAL ASSOCIATION, 

as Trustee

		
	By:	 	 /s/ Shawn Goffinet

	Name:	 	Shawn Goffinet
	Title:	 	Assistant Vice President


 [Signature Page to 7.00% Amortizing Notes Supplemental Indenture]