A power supply including a bi-directional DC converter and a control method thereof are disclosed herein. The power supply includes first to third terminals, first and second semiconductor switches and a mode switching circuit. The first terminal is electrically coupled to an external power source. The second terminal is electrically coupled to a load. The third terminal is electrically coupled to a battery. The first and second semiconductor switches are electrically coupled in series between the first and second terminals. The mode switching circuit is electrically coupled to the first semiconductor switch, the second semiconductor switch and a bi-directional DC converter, respectively. The bi-directional DC converter is further electrically coupled to an intermediate node between the first semiconductor switch and the second semiconductor switch, and to the third terminal.