it makes me upset when i see companies like HP using custom crap like combo USB / dc power cable.
The theory is going to be simple.... you will probably need an original cable to cut apart or look at how it is wired up on the scanjet.
USB is going to have four connections. +5v, GND, Data +, Data -. The combo cable probably is for +12v as well???? What kind of wall wart power does it use.