You have to find out how much current it draws first it should be listed on the fridge unit some place, then you just need a 12 volt power supply that can supply that much current (preferably about 25-50% more just to be on the safe side) You could either hack apart a 12 volt supply that meets your current supply and wire it directly, or buy a commercial unit that plugs into a wall and has a cigarette adapter. Any large commercial electronics store should carry them.