Also, keep in mind that a lot of car stereo shops will oversell wattage on cars... based on A x V = W, as stated above, a 2000watt Amp would require a 165A Alternator in a car. Alternators of this size are typically found on large diesel trucks, whereas 120A's on Pickups, and typically 60-80A on cars (stock). Cars/Trucks usually are 12Volts, to mimimalize the compexity of vehichle electrical systems.
You would probably be fine pushing a 1000watt PSU into the Amp, however check the 12V rails for maximum wattage, even if you got 700Watts, that would be about the maximum you could get from a car alternator if you never upgraded it. (Meaning little to no change from what was in your car, assuming no upgrades).
Also on fuses/breakers, typical homes with 15Amps have 14 guage wiring, and 20Amps 12 guage, do not exceed the maximum specification of Amps on the wire or you'll probably start a fire. Scratch that: You will start a fire if you exceed the amps/volts on a what a wire is specified at.