A power supply has first and a second switch-mode power supply (SMPS) units, which both contain a transformer having a primary winding and at least one secondary winding, and a driver stage. The power supply furthermore has a normal operating mode, in which both SMPS units are in operation, and a standby operating mode, in which the first SMPS unit is switched off by a control voltage. In the standby mode, the control voltage is also used to reduce the switching frequency of the second SMPS unit, for example by means of a connection, which reduces the oscillation frequency of the oscillator of the second driver stage. In a preferred exemplary embodiment, the output of a first driver stage is furthermore connected via a series circuit to the oscillator input of a second driver stage, for synchronization purposes.