Question PC boots normally but Crashes Under Load. HELP!

[Fit_potato101]

As the title says.

A few days ago my PC crashed and didn't post. After a little Troubleshooting I figured one of my Ram Sticks was bad.
PC booted perfectly fine, I used it for about 2 days until I decided to play some GTA, and it crashed again. It kept on crashing on almost every game (CS : GO )

So I ran a stress test on the GPU...worked fine, CPU stress test ran fine and so did the memory test which again ran fine.

Then I ran the GPU and CPU test together, and done Crashed again.

Something of Note is that when it crashes it doesn't reboot, there is no BSOD, it just blacks out and crashes, and
interestingly the Power button has its back-light on but absolutely doesn't work, I HAVE to switch the PSU off and then on to boot the PC again.

I'm petrified of switching it on now that I suspect the PSU.

I need your help to confirm that it is definitively figure out whats wrong and if it actually is the PSU.

This PC is very very important to me and my work, if it turns out to be the PSU I'll be buying a new one,
the current one I'm using is an RMA upgrade I got from CoolerMaster( sick of this )
Replaced the first one for sort of grunting noises in the beginning the replacement came with the same problem but I didn't have the time to get it changed then.

Specs

2600X
Zotac 1070ti AMP Extreme
8GB RAM
Gigabyte X470 Ultra Gaming
CoolerMaster MWE 750 Modular 80 plus Gold

Any and all help is very very appreciated, thank you!

 

[Diddly]

It's probably worth replacing the PSU at this stage

 

[Fit_potato101]

It's probably worth replacing the PSU at this stage

Thanks buddy, I'm highly inclined to do that, will RMA the current one and sell if off.