Abstract: A universal plug adapter is provided plugs of different specifications to be selectively extracted and positioned to meet and connect an external wall socket. The plug thus supplies power to a railed recess, in which railed recess a rail-positioned socket having different specifications is installed and electrically connected, so as to form the universal plug adapter. Therein, the rail-positioned socket has sockets of different specifications for plugs of different specifications to insert. Additionally, the rail-positioned socket rail-positioned socket may be tailed with a functional electric device, such as a nightlight, an alarm, a wireless router, a USB socket or sockets of different specifications, for easy and convenient use.