I took one 500 watt psu and another 550 watt psu and hooked up the green and black wires to some hand made molex connectors so that i can hook them up together as a master/slave combo or use them as separate psu's. This way when you turn on the pc with the front power button, both of the psu's will power on and shut off at the same time. I do this to power my gfx cards and system fancs on 1 psu and the rest of the pc like mobo, optical/hard drives on another psu.