There is provided a power supply for an electrical device operable in active mode and in standby mode. The power supply comprises a transformer having a primary winding on the primary side and a secondary winding on the secondary side. The primary winding is connectable to an AC voltage supply and is arranged to comprise N turns when the electrical device is in active mode and more than N turns when the electrical device is in standby mode. Circuitry on the secondary side is arranged to provide an output voltage for the electrical device during active mode.