Abstract: A power supply has an outer shell and a retention bar. The outer shell has a rear panel and a cover. The rear panel has a socket and two guide slots. The cover has two pivot slots and two pivot mounts. Each pivot slot is formed through the cover adjacent to a corresponding guide slot. The pivot mounts are formed from and protrudes inwardly from the cover and have pivot holes formed therethrough. The retention bar is mounted in the pivot holes of the pivot mounts and has a clip and two protrusions. Therefore, when the power supply is mounted in a casing of a machine, the retention bar simultaneously fastens the power supply to the casing and a plug to the power supply.