Exhibit 3.125

State of Delaware

Secretary of State

Division of Corporations

Delivered 05:09 PM 03/14/2012

FILED 04:24 PM 03/14/2012

SRV 120311870 - 5124327 FILE

CERTIFICATE OF FORMATION

OF

NRG DISPATCH SERVICES LLC

1.             Name: The name of the limited liability company is NRG Dispatch Services LLC.

2.             Registered Office: The address of its registered office in the State of Delaware is Corporation Trust Center, 1209 Orange Street, in the City of Wilmington 19801, County of New Castle. The name of its registered agent at such address is The Corporation Trust Company.

3.             Organizer: The name and address of the sole organizer of the limited liability company is Lynne Przychodzki, NRG Energy, Inc., 211 Carnegie Center, Princeton, NJ 08540.

IN WITNESS WHEREOF, the undersigned has executed this Certificate of Formation of NRG Dispatch Services LLC this 14th day of March, 2012.

/s/ Lynne Przychodzki

Lynne Przychodzki

Authorized Person