I'm getting random, sudden crashes during gaming sessions across many different 3D games. The computer will shut down and restart, then hang at the motherboard screen without going into the bios. No blue screen. Just insta shut down during games. I have to manually cut the power using the PSU switch and then power back on.

The crashes are very random. I'll install a new game, play for 10 hours, then the game will crash. The game will take less time to crash after the first crash until the game will crash within minutes of starting a session. There doesn't appear to be any particular circumstance in terms of system load that correlates with the crash.

It's not my SSD, as this happens with any game across the several drives I have installed

RAM test: Clean.

GPU test: Clean.

Motherboard? If the mobo was a problem, why is the system only crashing during games?

CPU? Same question as mobo.

PSU? The PSU seems like the most likely culprit. Games are the most electricity-intensive thing I do. The randomness does seem like it could come from a failing electrical device.