A power supply apparatus includes a front panel, a rear panel and two left and right side panels which together form a housing. Opposed edges of a partition are connected to the front and rear panels to thereby divide the interior space of the housing into upper and lower chambers. The left and right side panels each have edges which are placed to abut against the corresponding edges of the other side panel.Components of a power supply circuit are appropriately distributed in the upper and lower chambers. Some of the components in the upper chambers are located beneath the upper abutting edges of said left and right side panels, and a cover is disposed to cover at least those components which are located beneath the upper abutting edges.