FYI the latest SteamOS release (just a couple of days ago) added an option to only charge to 80%.

Cisco c3850-12x48u is about $150 on eBay.

• 802.3bt (60watt) PoE on all ports
• 36x 1gig rj45 ports
• 12x 1/2.5/5/10gig rj45 ports
• Has a module slot that you can add 4x or 8x (8x is rare so expensive) 10gig sfp+

The main problem is the idle power consumption. About 150w with nothing plugged in.