An exemplary adaptor circuit of a power supply includes a power connector, a first electric switch, a second electric switch, and an output terminal. The power connector includes a power good pin and a power pin. The first electric switch has a first terminal connected to the power good pin of the power connector, a second terminal connected to the power pin of the power connector, and a grounded third terminal. The second electric switch has a first terminal connected to the second terminal of the first electric switch, a second terminal connected to a first voltage terminal via a first transmission line or a second voltage terminal via a second transmission line by selectively mounting a connection component to close an open segment of the corresponding transmission line, and a grounded third terminal. The output terminal outputs a driving voltage signal to chipsets on a motherboard.