There are online tutorials for testing power supplies using a voltmeter. It sounds like you know your way around electrical testing so google how to test a power supply using a multimeter and hopefully you will have your answer as to whether or not it is your power supply. If not, you could buy the cheapest 750w power supply as a 'tester' just to see if you can play the game with a different power supply. If it turns out that you can play fine with the cheap power supply, then and only then would I invest in a gold or platinum rated power supply. I usually keep a few cheap power supplies to use for testing as I am not good with a multimeter.