Power-over-Ethernet is for more than IP phones, Wi-Fi access points and surveillance cameras. It can be used anywhere there’s a low-power device that would benefit from continuous power and the reliability of Ethernet connectivity. Assuming your network switch (or POE injector) is connected to a UPS, POE allows the attached devices to remain powered in the event of a power failure.
In my home and office, I use POE to connect and power a number of Raspberry Pi single-board computers configured as music players. The RPi3 B+ isn’t natively POE capable, so I use a POE splitter like the one pictured here.
Given a POE-capable switch upstream, this wee splitter provides 5 VDC at up to 2.4 A via a standard micro-USB connector. This model from Anvision is under $10. A 4-pack is just $37 on Amazon.com.