Desktop turns off when playing demanding games

[LudinK]

So just recently my pc began to turn off after a few mins of playing demanding games. I have played hours straight of fortnite or league of legends on max and it never turned off however when i tried to play rainbow six siege for the first time in maybe 2 weeks, it turned off. I tried to play it on lowest settings and still, it turns around the same amount of time. I then played league for some time and no issue. I decided to play sniper ghost warrior 3 on maxed out settings and at first it didnt turn off so i left it playing and i started a match of league with SGW3 running in the background to see if it would still turn off but i had no issues. After the match of league i continued SGW3 for about 3 minutes and again my pc turned off. I was thinking its maybe my PSU but i was wondering how someone could check to see what the issue is. I had played rainbow six siege a lot in the recent months/weeks so this issue just began.
SPECS:
AMD FX8350
Corsair 80i CPU cooler
R9 390 8GB
16GB ram
860 EVO 500GB
Corsair TX750
NZXT phantom 530

 

[ElectrO_90]

Classic problem of PSU, but you can only test this by borrowing a friends or buying a new one.