An adaptor for adapting a mains plug according to a first national standard to a mains socket according to a second, different second national standard. The adaptor comprises a housing with a socket for receiving the first mains plug, and at least two plug assemblies according to different national standards, one of the at least two plug assemblies being according to the second national standard. An externally-operable selection mechanism is provided for selectively deploying, or at least for making externally deployable, one of the at least two plug assemblies while simultaneously concealing, at least partially, the remaining plug assembly or assemblies so to make them effectively unusable. The end user can thus effortlessly select one of the outputs while hiding one that is not necessary. A network of internal conductors for providing electrical continuity between the first mains plug and the selected plug assembly is provided inside the adaptor.