Keep in mind a 500 watt power supply will not supply 500 watts on it's 12 volt line alone I'm asuming that's what you're intending on using. For example, a PC power supply I have sitting on my desk is rated for 200 watts. But the 12 volt line is only rated for 6 amps, which is only 72 watts. I think you need to very carefully analyze what the current requirements of the hardware you're currently using REALLY are and go from there, don't just look at the labels on the devices you're using, actually analyze the voltage and current that's being used.
Do a search in the forums, there was a thread not more than two weeks ago that explained the ins and outs of daisy chaining PC power supplies.