A switched-mode power supply (200, 300, 400) comprises a primary side, a secondary side and a transformer (103, 303, 403) therebetween. An output on the secondary side delivers an output voltage and an output current to a load. An output voltage control circuit (110, 113, 801) keeps the output voltage at a first level, corresponding to a first output current value. A circuit element (201, 301, 401) integrates over time a voltage obtained from the transformer (103, 303, 403) and produces a signal indicative of the integrated voltage, corresponding to a second output current value that is smaller than the first output current value. An output voltage modifier (113, 601, 801) responds to the signal by changing the output voltage from the first level to a second level.