I really like my seasonic PSUs. Quiet and no problems, "modern" selection of connectors and lots of power available on the rails. In spite of Skuzzy's insistance that it's a problem, I like the modular one I have. Yes every plug you add to a line drops the quality of power delivered down that line, but for most users the fact is that it simply isn't a problem. We're not loading the PSU up to 90% of capacity and holding it there, we're not running 3-way SLI, and we're not pushing for world-beating overclocks. A modular PSU will cost more but you really save on the clutter and you might even end up with LESS total connectors since you can often run single-connector lines straight from the PSU to the components needing power. The mobo will always get power straight from the PSU without any extra connectors since the mobo lines are permanently attached as usual, and you can often use dedicated lines to power various items instead of putting multiple items on a single line if you're worried about power quality. My video card uses two dedicated lines from the PSU, meaning each card is getting power from a line that has a single high quality connector (not those crummy molex ones). That means I'm probably getting better quality power than someone who has their vid card running off of a line that has 2 or 3 connectors on it.
As for your PSU being the culprit... A 650W psu wouldn't immediately strike me as being the problem since your total power load is probably somewhere under 350W at full load. Still, anything is possible I suppose and a crummy PSU just might give the results you see. Checking the exact PSU specs is a good idea, and matching the PSU to your vid card and then adding a hefty wattage pad is a good idea. Don't break the bank getting a tri-sli certified unit, but your PSU should be more reliable if it's not working too hard.
I'd personally wait for the vid card RMA. If the second card does the same thing, get a good PSU. PC Power and Cooling has good ones, but like I said I really like my seasonic PSUs. You really need to read some PSU reviews. Again it's against Skuzzy's recommendation, but I like the testing methodology behind hardocp's PSU reviews. They test them at various loads, look at voltage, ripple, sag under load, etc., and they also take the suckers apart to find out who the actual manufacturer was and what quality level of components were used. Very detailed, and it might help you choose what brand and product line to get because sometimes they can identify when an expensive PSU is really just a re-branded cheapo model.
If you need a PSU NOW though, it's hard to go wrong with PC Power and Cooling or in my experience, Seasonic. There are other brands that don't seem to have a "cheapo" product line, but I did my research a while ago and settled on those two as my personal picks.
