Out camping this week. I had a small speaker and an I-pad plugged into the USB ports. All working fine. Sun was charging my solar panels and charging the camper battery. Then I plugged my Cpap machine into the 12V receptacle to charge up it's battery. The USB ports immediately quit working. However the 12V receptacle continued to work fine and no fuses were blown. I could not get the USB ports to work, no matter what I tried. I have a fairly new Grandby with a panel that includes the 12V cigarette lighter receptacle and two double USB ports below.
On coming home, I cut out the USB ports and tested the wires coming into them, and there was 12 volt power. So this proves the USB ports themselves blew out. I was wanting to change them out anyway to a better quality.