Computer resets itself under high loads

Hey so my computer will just automatically reset sometimes if I am running a game with kind of high demands. normally I can fix this by lowering settings but it still happens sometimes. no blue screen it just automatically turns off and on again.

I've tried to monitor things with hwinfo64 but the files always end up corrupted. my only ideas are either heat or my power supply dying, but when im monitoring heats they dont seem to be getting high enough to crash.

my power supply is probably 10 years old give or take so I am thinking that is probably the issue, but does anyone know how I could diagnose this properly? thanks