A power converter includes a DC power source, a transformer having a first winding, a first MOSFET and a PWM controller at the primary side and a second winding, a drive control unit, a current detection control unit, a comparator and a second MOSFET at the secondary side. The comparator has its input end electrically connected to the current detection control unit and its output end electrically connected to the drive control unit, which is electrically connected to the second MOSFET for synchronous rectification. The second MOSFET is electrically connected to one end of the second winding, having a body diode built therein. The second winding and the second MOSFET constitute a combination circuit electrically connected to a load that has a capacitor electrically connected thereto in a parallel manner. By means of the aforesaid arrangement, conduction loss at a low load is minimized, thereby improving the efficiency at a low load.