In order to increase efficiency, the invention provides for a switched-mode power supply (100), which comprises input connections (101, 102) for receiving an input voltage and/or an input current, output connections (103, 104) for providing an output voltage and/or an output current, a circuit arranged between the input and output connections for current and/or voltage conversion comprising at least one controllable switch, a control unit (200) for activating the at least one controllable switch by means of at least one pulse width modulation signal having a variable frequency and a variable duty cycle, and measuring devices (151, 141, 153, 143) connected to the control unit (200), at least designed to measure the input amperage, the input voltage, the output amperage, and the output voltage, wherein the control unit (200) is designed to monitor the efficiency of the switched-mode power supply (100) by means of measured values of the connected measuring devices, and to optimize the efficiency by means of a first digital control circuit by activating the at least one controllable switch. The invention further provides for a method for operating such a switched-mode power supply (100).