Unfortunately I can't figure out how to import the picture of this accessory from isuzuparts.com website (apparently copyrighted) and the picture is such poor quality that zooming in on it still does not make it possible to read the label on either the converter or the receiver. However the converter looks like the typical 4.5-6v converter that is used on any small electronic device that can also be used with batteries to enable you to plug it into 110v.

I have no idea what a 100v to 110v converter would look like.

Even if the receiver operates on less than 12v it could still be used with an inverter(as you pointed out) with the 12v system, or else connected to a battery pack.

This may be all academic as this accessory may not even be available anymore. Will advise what I find out.