Abstract: A method for operating a power supply unit for an electrical system of a motor vehicle, the power supply unit having an electric generator having a stator having a stator winding and a rotor having a rotor winding, as well as a field current controller assigned to the rotor winding for selecting the setpoint of the current flowing through the rotor winding; the electric generator being set into rotation without a current being specified by the rotor winding, thereby generating a starting voltage; at least one component of the power supply unit or of the vehicle electrical system being energized by the starting voltage.