A plug and socket assembly comprising (i) a socket that includes a mating means disposed thereon, and an electrical contact on the socket, and (ii) a plug that includes a matching means for mating with the mating means disposed on the socket, and a conducting terminal for coupling electrically to the electrical contact on the socket. The matching means is configured to be adjustable between a compatible mode and an incompatible mode. When in the compatible mode, the matching means allows the electrical contact to contact the conducting terminal, and when in the incompatible mode, the matching means substantially prevents the electrical contact from contacting the conducting terminal.