Power supply device for a hybrid vehicle having at least one x-by-wire system

The device has a traction battery (1) for supplying power to the electric motor (2) of the vehicle, an independent vehicle battery (3) for the drive-by-wire system (4), a monitoring unit (8) that monitors the supply to the drive-by-wire system from the vehicle battery and produces an error signal if there is insufficient power and a control unit (5) connected to the monitoring unit that receives the error signal and releases power for the drive-by-wire system from the traction battery in response.