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