I've also been embracing Power-Over-Ethernet where appropriate[2], to prevent excessive breeding of wall-warts.
Every day is a school day.
Do you need to install special cable to do that then? (I assume it's not just your bog std Cat5)
Bog standard cat5. The device needs to be designed to accept PoE (802.3af), and you need either a switch that can supply PoE (which nearly always means a big one with evil noisy fans) or a mid-span power injector. Ethernet ports are transformer-isolated, and PoE intercepts the cable before the transformers to supply power.
You can sometimes bodge it with non-compliant 'passive PoE', where you simply break out the two unused pairs in 10/100M Ethernet and stick DC power up them with readily available dongles or passive injectors. There's no proper negotiation of current draw, no guarantees about voltage drop in the wiring
[1], and you can't esaily do it with gigabit, which uses all the pairs. Often useful, but proceed with caution.
Most proper PoE kit tends to be things like IP phones, CCTV cameras and WiFi access points, where a separate wall-wart is either impractical (eg. because it's going on a roof) or an unwanted cost/point of failure (if you've got a couple of dozen phones in an office, better to just have a single power supply to worry about).
As with so many rubbish things in life, assorted non-802.3af-complaint 'standard' implementations proliferate (Cisco, Ubiquiti, etc.).
There's probably a parallel universe where WiFi wasn't invented, where this became the de-facto standard for charging laptops.
[1] 802.3af uses 48V to provide headroom and minimise I2R losses, while still qualifying as extra-low voltage for safety purposes.