I have a 1250 watt power supply on a typical circuit and it's just fine.
Another thing, just because you have a 1000 watt unit, that doesn't mean it's using a 1000 watts when you turn it on. A 1000 watt power supply has the potential of supplying a 1000 watts of power, but it only supplies what is needed for the task at hand.
As an example, think of your house and it's appliances as a PC and the Power Company as the Power Supply. The Power Company has the potential to supply millions of watts of power, but when you switch the Main Circuit Breaker of your house to the On Position it doesn't supply a million watts to your home, it only supplies what you need.
Edit:
The wattage is being determined by the volts being generated, mainly 12 volts with a PC Power Supply (thou a few other voltages are being generated, 5 volts, 3.3 volts).
watts = volts x amps
1000 watts = 12 volts x amps
amps = 1000 watts / 12 volts
1000 watts = 12 volts x 83.3 amps