Question PC restarts under heavy gaming load ?

[baconStrips1111]

System:

Motherboard: EVGA X299 Dark, LGA 2066, Intel
CPU: Intel Core i9-7900X
CPU-Cooler: be quiet! Dark Rock 4
Memory: G.SKILL Ripjaws V Series (4 * 16) @ 3600MHz
PSU: EVGA SuperNOVA 1000 G3
M2: Samsung 500GB 980 PRO
M2: Crucial 1TB P1
HDD: Seagate 2TB IronWolf Pro
GPU: EVGA GeForce RTX 3080 Ti XC3 GAMING
Monitor: Dell Ultrasharp 27" , 4K @ 60 FPS
Case: Fractal Design Define 7

Preface:
I am running Linux as my primary OS on the 1TB P1 M.2 and as my secondary OS, Windows 10 on the 500GB Samsung M2, which I use manly for gaming and some 3D-modelling.
Recently I changed my GPU from two 1080ti's to a 3080ti and replaced the CPU cooler to the bequiet one.

Issue:
Even before that update using my 1080ti's I lately had sudden, complete reboots on titles like COD-MW on Windows. Meanwhile the Heaven Benchmark as well as older titles such as Hitman2 would run at max settings w/o an issue.
Since GPU prices dropped I decided to buy a new GPU (3080Ti) as well as the new CPU cooler (bequiet). Under Linux I can run the Superposition Benchmark for hours on end w/o any issue, and on the fresh install of Windows as well as all of the required drivers the machine still crashes and reboots under load of modern titles. With COD-MW as well as Metro Exodus @ 4K, the machine simply restarts after starting the game.

Questions:
I am a bit puzzled by the situation, but suspect a hardware failure, more precisely I suspect my PSU to be the culprit, but its mounted correctly, and its only merely 3 years old.
Since the issue arose already from my older 1080ti's and still persists with the 3080ti - it could also be the motherboard - or the cooling of the case?
If anyone has a clue what I should look / exchange first that would be helpful! Thanks!

 

[KananX]

I think it could be the CPU, more precisely the mainboard. Why, because while full GPU one sided usage with the benchmark is fully stable, once you start a CPU demanding game like COD it crashes. To be sure you can try out Prime95 and see if the CPU is stable. But yes, could also be the PSU, even if unlikely.

 

[baconStrips1111]

So after I went home and tested my CPU on Prime95 it is stable on its own - I also test Furmark on 4K and it is also stable, it never becomes hotter than 82C.
However after using Prime and Furmark the machine instantly crashes. I use a Air Cooler and the fins practically touch the GPU - could that be an overheating issue? Or is it simply the PSU? Thanks!