PC Shutting off then back on while gaming/under load

[ali13245]

The title says it all. Basically if I am playing a game like the witcher 3 or battlefield 1, my pc just randomly shuts off (not windows shutdown) and then turns back on. Its like a power cutoff type of shutdown. It happens randomly. Sometimes it can happen in a few minutes, other times it can take an hour or more. The PC is fine all day when doing simple tasks such as web browsing, youtube, etc...

Here are my specs:
i7 4790k @stock speeds (No OC)
2 x GTX 980's @stock speeds (No OC)
16GB corsair vengeance ram @2400MHz (XMP profile)
MSI Z97 Gaming 7 motherboard
Corsair RM750 PSU

My PC is custom watercooled, so I have no reason to believe that temps are causing this issue.

Temps while playing The Witcher 3 @1440p ultra settings:

CPU: ~50-52 Celsius
GPU1: ~49-51 Celsius
GPU2: ~47-49 Celsius

I have had this PC for 2 years and 6 months now. I am running into this issue just now. Please let me know if you need any more information on the system.

 

[ko888]

At one time some customers found that their Corsair RM750 or RM850 would shut down due to thermal problems under certain conditions.

 

[ali13245]

So I ran aida64 for 6 hours last night, and when I woke up he PC was still on, so I guess that eliminates the CPU? I left my house about an hour ago while running heaven benchmark on a loop to determine if its a GPU issue. Prior to doing all if this, I actually ran both aida64 and heaven to stress both CPU and GPU's and that recreated the problem. So I'm hoping it is a Power supply issue, because I can just RMA and be done with this. I already opened a ticket with corsair customer support, currently waiting to hear back from them. Is it possible for a PSU to show signs of degredation from just 2 1/2 years of use?