Noctia

GPU core memory controller and VRAM both can cause artifact, depending on the VRAM modules used on your graphic card they might not be very high compatibility for you to OC them 2 well together in the first place.
 
Is a hard to diagnose scenario because sometimes games don't artifact will still crash, and stress test program don't guarantees everyday gaming stability until you encounter a game crash, read graph for the last utilization spike or sudden drop before crash. Tune down something, stable the power delivery in Nvidia CP, and continue your days on. It can take months to findout a stability for all the games.
 
The best game i used for testing GPU/VRAM stability was Witcher 3. 3DMark and Heaven stress test would pass my OC and all games run fine except Witcher 3 will crash until i reduce VRAM to a near complete stock speed. Eventually i got tired and not wanting my VRAM to melt just to leave my expensive working GPU core render useless, nowdays i just run OC GPU and leave VRAM stock, no artifact, no crash, no worries.

Trust me get a grounded outlet. I have an old PC without one and I have regretted even touching it one too many times..

The issue is it can potentially build up a large electrical charge, while small ones make it uncomfortable to touch it can be large enough to give you a really nasty shock. Not to mention if something were to go wrong say with the PSU like short to the metal casing, it would be at mains voltage if one were to touch it. Your best bet is to look for a plug in the home that is grounded, test using an outlet tester to make sure it's properly wired, and use an appropriate extension cord for it.
 
If your comfortable working with electrical you can take off the outlet to see if the wiring is grounding wires in the outlet box, if there is it's a simple matter of changing out for a 3 prong outlet, if not then it can get more complicated.

Two to three prong adapters are a good option as long as you can ground that lead that comes off of it properly, it shouldn't fry anything per say as it's not directly shorting something out. In terms of the PSU thing it wasn't the case of loose wires but just a possibility of it failing catastrophically and shorting to the casing.