What model hub did you buy? If it has an external "wall wart" type of supply, it should say what the output voltage and amperage is, as well as the plug polarity. Take that info down to to your friendly neighborhood Radio Shack, and find the 12v DC-DC convertor that matches those specs. Take the hub as well so that you get the correct sized coax connector. If you can get the version that has a short cord between the cigarette lighter plug and the DC-DC transformer, it will be much easier to hardwire into your car's electrical system.