I have found mine. It's a Sunpak GT9 and it has a two pin connector at the top. Next to it is a switch marked AC and BATT. In the battery position it moves a piece of plastic over the AC in area. This woulds prevent it being switched to battery if a mains plug was inserted.

There is a second switch to set the voltage. 100-120v in one position, 200-240v in the other.