1440 Watts would be the theoretical maximum for a standard 15 A 120 VAC receptacle, and that's assuming you're not running anything else off that same branch circuit.Whatever you get, check the amps and make sure you aren’t pulling too much for the circuit.
Watts/ Volts equals amps.
Remember that a nominal 15 A breaker can not be operated at more than 12 A on a steady-state basis.
P = IV
1440 W = 12 A * 120 V