Bad PSU or Motherboard?

[Etrious3422]

Hello Linus Tech Tips Community, I seem to have a dire problem on my hands.
I recently had to get rid of my MOBO and PSU to accommodate a new processor I had received along with a new Graphics card. And me being the cheapo techie, decided I'd risk open box parts. The motherboard was an easy problem to solve, it was missing a screw for the mounting tabs. (990FXA-UD3 R5 From Gigabyte, nice and stealthy black looking. :3) But there seemed to be nothing wrong at least with the PSU at the moment of using it.

Now I recently upgraded to a water cooling loop I made to test some overclocking, and that involved transplanting all the parts I had into a new case. After that I'm getting weird startups where when I press the power button, and it flickers to life, but shuts down after a second or two, then comes back to life just fine.Then the main problem is that under a ton of load, like in a game of sorts, the computer crashes in a way I haven't seen before, where a screen of grey and black bars go across one monitor while the other monitor in my selection goes white, leading me to believe it was the two crossfired cards I have.

After extensive tests done with my buddies system, and 100% load stress tests on both of the cards for around 24 hours... I determined it wasn't them.

I'm stuck between the PSU possibly being faulty and not being able to output its wattage correctly (RM750 PSU From Corsair with 80 plus gold)

Anyone else get this strange problem?

Full system specs are:
AMD-FX 8320 Black Edition CPU
2x8GB Crucial Ballistix RAM + 2x4GB Crucial Ballistix RAM
Gigabyte 990FXA-UD3 R5 Mobo
2x R9 270x's
Corsair RM750 PSU
EK custom loop. (I checked for leaks through this whole thing, and no leaks even after days of shifting it around)

[Etrious3422]

SO I just booted up speedfan to adjust radiator fans speeds when suddenly, my 3.3V dropped to 2.46V Guess its the PSU then.