A power supply assembly includes an enclosure body, a cover panel mounted to the enclosure body, a power supply unit, and a positioning element. The enclosure body includes a bottom panel, a rear panel, and a side panel. The power supply unit is mounted in the enclosure body and is prevented from moving in a first direction substantially perpendicular to the rear panel and a second direction substantially perpendicular to the side panel. The positioning element includes a plate body, a first positioning portion, and a second positioning portion. The power supply unit is sandwiched between the bottom panel and the plate body. The first positioning portion is for preventing the power supply unit from moving along a first direction substantially parallel to the bottom panel. The second positioning portion for preventing the power supply unit from moving along a second direction parallel to the bottom panel.