A power supply assembly includes an enclosure body, a cover panel mounted to the enclosure body, a power supply, and a positioning element mounted to the cover panel. The enclosure body includes a bottom panel, a rear panel substantially perpendicular to the bottom panel, and a side panel substantially perpendicular to the bottom panel and the rear panel. The power supply assembly is mounted in the enclosure body and is prevented from moving in a first direction, that is substantially perpendicular to the rear panel, and a second direction, that is substantially perpendicular to the side panel, and disposed between the bottom panel and the cover panel. The positioning element includes a first ladder-shaped positioning tab abutting two adjacent surfaces of the power supply and preventing the power supply assembly from moving in a third direction, that is substantially perpendicular to the cover panel and the second direction.