Hey guys this has been plaguing me for weeks and I think I finally have pinpointed the issue. My PC will randomly shutdown while gaming but only sometimes. It would go weeks sometimes without shutting down then other days shutdown back to back 4 times in a row as I loaded a game a couple minutes into the match. 
 
After a ton of troubleshooting I have finally found the culprit which is most likely the PSU. The reason it was not suspected was because it would work perfectly fine when stress testing no matter how long I left the stress test go. However, I downloaded a program called OCCT that has a specific PSU test and the moment I run that my PC restarts. I think it is from the built in protection on the PSU according to other threads on the internet talking about the OCCT test restarting PC's. To confirm this I ran both a CPU test (prime95) and GPU test (furmark) at the same time. The moment I hit go on Furmark after prime95 was running the PC did the exact same thing. 
 
The question now is, is the PSU broken or do I need more juice. I plugged all my components into a calculator and it says the most I would ever need should be 650w. The PSU I have is "EVGA SuperNOVA 850 Ga, 80 Plus Gold 850W, Fully Modular, ECO Mode" (amazon title)
 
my PC Specs are i9-10900k / 2080ti / z490e MOBO / 64gb RAM (16 x 4) / 3 NVME drives / 6 Corsair Fans / Kraken z53 / and an Internet Card. 
 
I got this PC built by Microcenter over a year ago with most of the parts coming from their recommendations. Didn't want to reorder the same PSU if its gonna have the same problem but not sure how to know what I can easily upgrade to without having to rewire stuff. 
 
 

They had some issues with the GA series units that required an updated one be made / exchanged - mostly because of the new 30xx series cards were showing the problem by their extreme need for juice.... 
So sounds like yours is in definite need of an RMA .
 
Have the issues with SuperNOVA GA series and RTX 3000 series cards been fixed? - EVGA Forums
 
850GA + 3080 TI = over current? - EVGA Forums
 

I had the same issue when playing MSFS. The game generates power spiked which caused random shutdowns. I changed my psu to a larger capacity and the problem was resolved. 

I remember during my first build I bought a used psu, before I knew much about computers.  I finally got all my parts and finished the build.  When I turned the pc on for the first time nothing happened.  Of course I panicked because I had no idea what happened.  I was not sure if I incorrectly installed something wrong.  After a few days of trial and error I found that the psu was dead.  It seems like people that thier computer randomly shuts off is because of the psu

Well, I will tell you that I had issues with my 850 GA where my games would drop down to around 2fps constantly. I RMA'd the 850 GA and they sent me another 850 GA. Had it less than a week and after about 10 hours of gaming the same issue popped up. Then today I turned on my PC, loaded up a game and roughly 10 seconds in the entire system shut down. These power supplies (850 GA) need to be recalled because there's a big issue with them. Now I'll have to wait another 2 days for EVGA to respond to my ticket.

Issues on this PSU are all over the internet. Why they continue to sell them is baffling.

I would suggest that you sue the company, or join the lawsuit that I have filed, regarding the deceptive business practices and defective products made by EVGA 

drive.google.com/file/d/1fSlGp4sz6_3rQ4jOh4iNbNMYnhrI-ez_