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.