A power extension wire includes a power plug, a socket, and a cord connected between the power plug and the socket. The power plug includes a first temperature sensor element, the socket includes at least one alternating-current jack. The cord includes a plurality of alternating-current conducting wires and at least one direct-current conducting wire. When a temperature sensed by the first temperature sensitive element is higher than a first threshold value, the first temperature sensor element transmit a first sense signal to the socket through the at least one direct-current conducting wire.