Abstract: The socket has a housing, an outer sleeve on the housing centered on an axis and having an axially extending and radially inwardly open groove. A latching element in the housing in axial alignment with the groove is displaceable axially relative to the outer sleeve. A spring or other biasing unit is braced between the latching element and the housing for urging the latching element into an outer position and a mechanical coupling between the latching element and the switch prevents a switch on the housing the switch from moving from its the position to its on position except when the element is in an inner position. A nonmatching plug has a body formed with a radially outwardly open recess and respective contacts in the body are engageable with contacts of the outer sleeve. A tubular adapter body is fittable over the plug body and inside the outer sleeve in an inserted position with the plug contacts engaging the socket contacts.