Jesus Echavarria wrote a how-to on adding a USB power port to a switch:
I want to start some projects with Arduino and IoT, so the first things I need is an Arduino board, an Ethernet shield and a switch to connect it to the net. Also I need a power supply for the Arduino board, and I think that, better than a external USB AC wall adaptor or power supply, is modify the switch to add it a USB power port that can power the Arduino board. I’ve got at home a TP-Link TL-SF1008D, a simple 8 port 10/100 Mbps switch. So, let’s go to open it and add it the USB port!
More info at Echavarria’s blog.
Via the contact form.
but doing this means that your Thing of Internet is stuck right next to the switch; it’s why we have PoE!
In related puzzlement, why all the hacker-friendly ethernet adapters (shields etc) do not support PoE I do not know. It would make them 10x more useful.