The problem you're describing is very unlikely to be caused by a power issue - There are PSU calculator tools available, but they're only guides, and should be looked at more as a 'minimum spec', which we all know should be taken with a pinch of salt! One example is here -
http://extreme.outervision.com/psucalculatorlite.jspYour FPS issue - Is this in gaming? Or do you see it most elsewhere?