A better solution is to get a 400w supply and then get a battery UPS that it plugs into. That will condition and regulate the power that gets fed into the box.

Even if you have a 500W+ power supply.. it will still crash if the power fluxuates. This is a common cause of computer malfunction. The battery solution helps with power dips and protects against spikes. My 3 computer rig runs much more stable since I have it all plugged into a big mother battery backup. Coincidence?.... I think not...