How can I tell if it's the card or the power supply?

What power supply? Can you test with a lower power graphics card or test the graphics card in a machine with a stronger PSU? How are your games crashing? Exiting out with a message on the screen? Or BSOD or system shutting off when you try to play?

Power supply is the raidmax 630ss (yes, I've heard Raidmax is bad news but I've also heard people running their gtx 260s on the 630ss so I can't immediately blame the psu).

I can't test it with a lower power card, the gtx is the first card I've purchased that needs pci-e cables (or any, really. My other card is a 7600gt). I don't have a stronger psu.

The games crash with no message, usually through some sort of graphical anomaly. Street Fighter 4 crashes by displaying a texture full size on the screen (as the texture might look if you opened the texture in photoshop or something, all flat, before it is mapped to the mesh). The system doesn't shut down or blue screen, I can usually quit the program and go about my business.

Thanks for your help

i wouldn't use the raidmax for a second more, try to find somebody that has a system running and test your card in that 9or borrow their PSU)

There is no utility to monitor the power being used by your vid card.

1) If you installed the new psu and the new vid card at the same time, put the old vid card back in and see if it crashes.

2) I can't find a picture of the business end of your psu - manual and gallery on raidmax home page give me nothing. So, can you try using a different socket to plug in the PCIe connector cable on your psu?

3) This smells slightly more like a bad vid card than a bad psu, but psus do lots of funny things. Can you "loan" the vid card to a friend to use? See if it crashes in another system?