Question PC restarts whenever gpu is under load

[xNatteFrostx]

Trying to figure out what is going on with a used PC I bought online.
Whenever I try to run a stress test (furmark) the PC shuts off then tries to start up over and over again, before it can even show post it restarts. Tried 3 different GPUs with the same results.
Voltages all show they are all okay while PC is idle.
PC specs:
I5 6600 non k
2x 8g Corsair ddr4 ram
ASRock z170 extreme 4
EVGA 500w 80+ white PSU

 

[rgd1101]

tried a different psu?

 

[xNatteFrostx]

I did and furmark actually worked with no restarts. So I'm going to assume it's the PSU.