Ac adapter and electronic apparatus unit

An AC adapter includes a conversion part, an output terminal, and a voltage adjusting circuit. The conversion part converts alternating current input to an input terminal into a direct current. The output terminal supplies the direct current to an electronic apparatus outside. The voltage adjusting circuit lowers a voltage of the output terminal by a predetermined voltage from a regular supply voltage in a term after the AC adapter is connected to the electronic apparatus until a predetermined time lapses.