A clocked power supply unit with low-voltage output for direct current includes at least one secondary winding of a transformer, a rectifier connected to the secondary winding, two outputs upon which a predefined output voltage is able to be tapped, and a shunt which is configured to provide a voltage signal which is proportional to the output current, wherein electrical measurement contact points are provided at which either a measurement voltage proportional to the output current and diverted from the shunt, or a measurement current diverted from the shunt, may be tapped from outside the power supply unit via the test points of a voltage and/or current measuring device.