We have also used automotive USB power converters to power USB and other 5V devices on both our competition and non-competition robots (e.g. t-shirt cannon); you can get these at almost any local convenience store. (
Example). It is usually a simple matter to remove the power port connectors and expose the wires to provide the 12V input. There are also units with
wire pigtails or
spade connectors for inputs, designed for installing in a dash board; a bit more effort to locate, but neater-looking.