The power of a circuit device depends on the potential difference (p.d.) across it and the current in it. The p.d. is the energy transferred for each coulomb of charge that passes. The current is the charge that passes each second. Together they decide how much energy is transferred each second, which is the power.
So the power in watts is found by multiplying the current in amperes by the potential difference in volts. A bigger current means more charge passes each second, so more energy is transferred each second. A bigger p.d. means each coulomb of charge transfers more energy. Either one makes the power greater.
If the p.d. doubles and the current stays the same, the power doubles. If the current doubles at the same p.d., the power also doubles.
Example: a motor with a current of 3 A at 12 V has a power of 3 × 12 = 36 W. A mains kettle with a current of 10 A at 230 V has a power of 2300 W. A 12 V lamp with the same 10 A current would have a lower power of 120 W.