An active output compensation circuit is adopted for use on a power supply which receives input power and regulates to become a plurality of different output power. The power supply has a transformer to transform the input power. The transformer has a secondary side connecting to a plurality of output regulation units to deliver the output power. The active output compensation circuit includes a voltage difference judgment unit electrically connected to the output regulation units and a plurality of compensation channel switches. The compensation channel switches bridge two output regulation units and the voltage difference judgment unit. The voltage difference judgment unit judges the voltage difference of two output power and determines whether to output an ON signal. The compensation channel switches are driven by the ON signal and set ON so that one output power can compensate another output power.