There might be a fuse in the receptacle somewhere like a small cylinder type. I doubt they would have a fuse in the fuse panel area in the RV. It’s possible there is a loose or broken wire or solder in the usb receptacle itself. It would be nice if you could just swap it out or maybe put some test leads on the back from a multi meter and confirm you have power.
My RV is a couple years old now and I just have a single two usb outlet that is wired to my 12v system because it works when not on shore power.
make sure that the source of this problem is not with the USB cord you are using. Some times my cords work on one adapter/receptacle, and not another. I've thrown away many cords and receptacles because they simply stopped working altogether. And as noted, it may well be the receptacle that is the problem.
Amazon sells a small plug in DMM so to speak, shows volts and amps,, I use them in the ac /dc blocks at home USB have a life span of 1000 to 1500 plug in according to the internet. I would take the socket out and use a multi meter and see if 12 volts even goes there,, seems Dutchman is pretty useless,,in the 5 years we have owned a TT,,, good luck,, once you find out if you have 12 volts, it is just a regulator to make 5 volts.. no 12,, no 5 volts.