I have a number of Dell Wyse 3040 thin clients (5v version, there's also a 12v version) scattered around my property. I've converted two of them to PoE by the simple expedient of buying a USB PoE splitter, cutting off the USB connector, and soldering on the appropriate barrel connector (for future searchers: 4mm x 1.7mm, pin == positive). I also just purchased some pre-made USB-A to 4mm x 1.7mm cables to try out on the rest.