Power supply system for a vehicle, in the case of which an onboard voltage supply system for supplying electric consuming devices can be fed by at least one power accumulator, and in which external electric consuming devices can be connected to the onboard voltage supply system. At least one portable removable accumulator, which can be charged by way of the onboard voltage supply system of the vehicle, is provided, which removable accumulator is constructed as an energy accumulator expansion unit controllable by way of a battery management system, by way of which energy accumulator expansion unit electric consuming devices, which are part of the vehicle and/or external electric consuming devices, may be operated, so that the removable accumulator can optionally be utilized as a stationary power supply device in the vehicle when the onboard voltage supply system is connected or, when the onboard voltage supply system is not connected, can be used as a mobile power supply device independently of the vehicle.