I know this is stating the obvious, so what have I missed. A normal USB socket on a PC is rated at 500mA. A phone, or any other device, plugged into this shouldn't pull more than 500mA or it risks damaging the PC. Surely this means that the manufacturers of the car chargers are latching onto this & using this over current protection, to stop there 5p voltage regulator from being melted. If you short out the pins & take away this protection, the poor little cig charger is going to give up very quickly, as it's not meant to cope with the sort of current that will be demanded.