If you found it for free, keeping hooking up higher voltage till you get something out of it. If you need a large amp 12V source get you an old dead battery, make sure its filled up with fluid(water/red wine) and hook it up a cheap battery charger. the old battery ought to help store some capacitance and help get rid of the ripples from the battery charger, assuming it's a cheapy. or if you need a slightly less amperage 12v use an old computer power supply, yellow and black 12V.