PURPOSE: To selectively form DC power sources of various specifications to be supplied without switch operation by inserting a power source information unit attached to an electronic apparatus to the power source information unit socket of a power source adapter.

CONSTITUTION: A power source information unit PIU is engraved on upper and lower parts with power source information having selective meaning in response to the uneven state. A power source information reader RPIU reads power source information, i.e., DC voltage information IDCV, DC current information IDCI and DC polarity information IDCP from the unit PIU inserted to a power source information unit socket SPIU, and transmits it to a controller CTLU. The controller CTLU controls the operations of an AC-DC converter ADCV and a DC output selector POSW. That is, the information unit attached to an electronic apparatus EEQP is merely inserted to an electronic information unit socket to selectively and automatically obtain the DC power source to be supplied to the apparatus EEQP.