A circuit for displaying failure information of a power supply unit supplying power to a central processing unit includes a controller including a random access memory (RAM) to store failure information of the power supply unit, a DC power circuit, a processing unit connected to the controller for reading the fault reasons stored in the RAM, and a display unit to display the fault reasons. When the power supply unit does not operate, the DC power circuit supplies power to the controller, such that fault reasons stored in the RAM will not be lost.