Standard USB is 5V 500mA, though higher currents are possible if both the supply and device support it. The cheap Poundland type cigarette lighter plugs are nominally 500mA. Devices need not draw the full 500mA available, and it's perfectly normal for them not to do so.
You can build your own hard wired supply with just a 7805 and a cable with a female USB socket ('receptacle' in USB terminology) on the end of it. Info on USB cable connections is easily available if you google. There are only four wires in a USB 1.1/2.0 cable, a twisted pair for the data and +ve/-ve. You don't need smoothing as such but you will need to decouple the supply with something like 220uF. It's good practice to add a diode to protect the regulator, as shown in the standard datasheets.
https://en.wikipedia.org/wiki/USB_(Physical)