How does dual PSU's work?

I'm purchasing a Coolermaster CM Stacker, which can house 2 power supplies, and comes with the necessary adapter. I've read deception's DFI nForce4 thread, and because I'm getting the new DFI nForce4 board, I would like lots of juice going through all the components. I have my eye on a couple of OCZ Modstream power supplies, but I'm not really brushed up on this dual power supply concept. Because deception has recommended at least 30A on the 12v rail, and the Modstream has 26A, does having 2 psu's effectively double the power on each available rail? Would I be safe buying two and having an effective overclock?

Thanks

Dime