Right, that makes more sense.
You'll need a dedicated 12v Power Supply, but for that amount of power there is no way you'll be wanting to use your computers PSU for that.
Running a 1500w amp will be hard though, you would be spending crazy amounts of money on a power supply for that. I would recommend getting an old car battery and charger and wiring that up as an intermediate current dump, that would be the cheapest option.
If you've not comfortable with electronics though I wouldn't recommend this, perhaps look into getting a proper mains supply (120v/240v) amp to hook the subs up to instead.