The power supply is rated 550W continuous and is 80+ certified. I have an undervolted i7 930, two 1.5v RAM chips, and nothing else in the system that adds any significant load on the PSU (1 7200rpm HD, DVD drive, 3 80mm fans, the motherboard stuff, and... uh... I usually have a USB device plugged in). This calculator gives me a minimum PSU spec of 411W and 461W recommended when I put in my build with two 1GB GTX 460s. Compared to the test setups here and here and considering the undervolting (I'm not overclocking the video cards either and will undervolt those too if I can without lowering the clocks) it seems like my PSU could handle the total load.
My bigger concern is that I would have to run both 460s off of a 12V@25A rail (that's 300W). Official specs say this is too low, that the cards need 160 or 170W available each, but based on the tests it doesn't seem like they'd actually consume that much.
So... could I pull this off? What are the odds I could damage a component besides the PSU? The BP550 is under a good warranty and I would have to buy a new PSU anyways if it doesn't cut it.
P.S. If I do have to upgrade the PSU, any tips for getting an adequate one as cheap as possible?
P.P.S. Wait, if I buy a cable (modular FTW), I could run 1 card + drives on the 12V@25A rail and then I could use the 12V@22A rail I'm currently using for the drives on the second video card....
You can accurately determine if your current PSU has the proper wattage and 12v rail amps. and is a quality PSU that can meet the power needs of those two GTX 460's by following the link below. No guessing or speculation is required.