It's all about the inner workings of the PSU, such as the quality of the capacitors and voltage regulators and how it all plays into the level of protection and reliability that you get. If you read a few PSU reviews on Tom's Hardware, you'll see what I mean.
It's entirely possible it has nothing to do with your PSU, I'm just putting forward a possibility for you to consider based on stuff I've heard before. It might be worth returning your GPU for a replacement to see if you got a bad unit. Or maybe you could get one from a different brand to see if that makes any difference.