PoE Texas POE-IO-21 | Passive PoE Injector/Splitter Kit with 2.1mm x 5.5mm DC Connector and 10/100 Ethernet - Extend PoE Over Ethernet to DC Devices

Depending on distance (see http://wifiqos.com/poe-calc.html)
the power source could be the power supply that came with the wireless access point, IP video surveillance camera, etc.

This set contains
a very cost effective injector and breakout or splitter component
The injector inserts the DC voltage at the source location into the 5.5mm x 2.1mm injector plug
The DC voltage is then carried over the spare pairs of the 10BASE-T or 100BASE-T network cable
The breakout or splitter extracts the DC voltage from the network cable onto the 5.5mm x 2.1mm splitter jack

Other Options
Also available is a 1.35mm version WS-POE-IO-1.35 and the gigabit version WS-GPOE-1-WM