The switched mode power supply contains a transformer, which has a primary winding and at least one secondary winding, a switching transistor in series with the primary winding and a control circuit for controlling an output voltage of the switched mode power supply. The control circuit contains an oscillator, whose oscillation frequency can be set via a terminal, and which is coupled to a secondary winding of the transformer. The wiring for the terminal is connected such that the switched mode power supply starts up at a relatively low oscillation frequency once it has been connected, and, during operation when an additional voltage is supplied to the input via the secondary winding, the oscillation frequency of the switched mode power supply is increased. The terminal is connected in particular via a bandpass filter to a voltage generated by the secondary winding.