A power supply and an adaptor plug therefor, wherein a slot with a guide rail is provided at the bottom at one end of the power supply. Two body spring leaves connected to a circuit board of the power supply extend through and protrude from two body spring leaf holes in the power supply. The adaptor plug is provided with a guide groove. Two insertion leg spring leaves on the two insertion legs of the adaptor plug extend through and protrude from two insertion leg spring leaf holes on the adaptor plug. The adaptor plug is installed in the slot of the power supply by a joint formed by the guide groove and the guide rail. The insertion leg spring leaves and the body spring leaves contact each other.