Watt(energy) = Volts(voltage) * Ampere(current)
e.g. USB phone charger rated for 5V/2A = 10W, laptop adapter for 19V/65A = 1.2kW, electric heater rated 110V/15A = 1650W
Voltage and current are like height and width of a 2D box named wattage or energy, and you can stretch or shrink the height thus changing width, but not the total area