You have to convert the power to 48v and back down to whatever you need on the other end which has losses, plus you have losses over the cable too.

Well quite frankly 48V has lower losses than 12V

110v -> 48v (long thin cable) -> 12v

Versus

110v (long thick cable) -> 12v

Top has more conversions and more current running on smaller gauge

At higher power the Ethernet drops quite a bit of voltage/power compared to the wiring in your walls. Furthermore 48v vs 110v is double the amperage/more loss on top of that.

Then there’s double/sometimes triple conversion (120:48 and then 48:dc; 120:48 and then 48:12, and then 12:dc).

Furthermore magnetics are a must on both side of the PoE which also isn’t great.

At lower power there’s more circuitry to run and multiple conversions aren’t great compared to a simple cheap flyback.

For more technical feel free to check here, although it isn’t quite end to end: https://e2e.ti.com/cfs-file/__key/communityserver-discussion...