In an IP networking class we talked about the potential problems that 'non standard PoE' can be.
Maybe the most familiar example of this is Ubiquiti, who has a PoE method that does not use (802.3af/at) 48 VDC, but (nonstandard) 24 VDC instead:
In the past, this has been an issue for unsuspecting PoE users unable to power using PSEs built to meet the 802.3af/at standard.
Where else in the market is non-standard PoE used? Any other brands or products to be aware of?