There are many car chargers on the market that use a standard 5V USB plug. Some are rated at 500ma and others 1A.
There is one available at Jaycar at the moment that claims a 1.2A output. I recently purchased 3 different USB car cigarette lighter adaptors, and I measured the ripple voltage at various loads. The results were quite surprising. None of them had a ripple voltage of less than 100mV at 500mA, and at full load the ripple voltage was nothing short of attrocious. They probably only work because the phones themselves have filter caps installed to combat this.
These devices have become smaller and smaller, and the current batch sit flush with the cigarette lighter. So there is not much room for any filter caps or inductors. I wonder if Dave could use his universal dummy load that he has just built to do a few tests of common cigarette to USB adaptors.
This would be a cheap tutorial as the parts would cost less than $20, and some quick CRO shots woud be very beneficial for many users of these devices.