The standard unit of measurement of electrical power. One watt is one ampere of current flowing at one volt. Watts are typically rated as AMPS x VOLTS or VOLT-AMP (V-A). However, this rating is only equivalent to watts when it applies to devices that absorb all the energy, such as electric heating coils or incandescent light bulbs. With computer power supplies, the actual watt rating is only 60% to 70% of the VOLT-AMP rating.