For a DC circuit, P = E*I. But not for an AC circuit unless it has a power factor of unity.

Watts = volts * amps * PF, where PF is the cosine of the phase angle between the voltage and amperage. If there is no phase difference, PF is unity (1).

A (fictional) purely capacitive or inductive load will show a PF of zero. No matter what the current flow or voltage, there is no power consumption.