Abstract: A power adaptor including a body and a plug is provided. The plug includes an insulating housing and at least one blade partially inserted into the insulating housing. The insulating housing is connected to the body and includes a base and at least one extending portion extending from the base, a part of the blade protruding out from the base is partially covered by the extending portion. A distance between an edge of the base and the extending portion is D, an extending length of the extending portion is L, a thickness of the extending portion is T, and D2+L2=(D+T)2.