A power supply adapter includes a base plate, an electrical connector assembly disposed on the base plate, a support frame, a circuit board, and a shell body. The electrical connector assembly includes a hot connector assembly, a neutral connector assembly, and a ground connector assembly. When the adapter is plugged into a two-prong socket, the ground connector assembly is grounded to the two-prong socket. The support frame covers the electrical connector assembly and is affixed to the base plate. The circuit board is disposed on the support frame and electrically coupled to the electrical connector assembly. The shell body covers the support frame and circuit board and is affixed to the base plate. The power supply adapter can used with two-prong sockets that lack a ground slot, and provides grounding test function after being plugged into the two-prong socket, making it safe and convenient to use.