I don’t think I would trust anyone here’s answer. The only way to know is to to test it. Theoretical talk about ‘more conversions’ is kinda discounting the entire field of power supply design. We need someone to slap a killawatt on a system using PoE, and then do it again on that system using external adapters.
I tried Googling to see if anyone had done that and didn’t see anyone doing real testing (on the first page of google at least).
I do have these findings to report: 1) PoE is marketed as cost saving, largely on the install and maintenance costs: fewer cable runs for weird AP locations, less electrical work, etc. Which means we cannot assume that if PoE is in wide usage, that it is due to electricity cost savings. And 2) increasing efficiency of newer PoE power supplies is an active area of development, meaning that a particularly old set of PoE hardware might be less efficient than expected.

My thoughts are:

• With PoE you’re doing 2 conversions which could waste more power, AC to 48V at the switch, and then 48V down to whatever the device needs with it’s internal buck converter. You also have slightly more losses on the longer run of low voltage 48V DC through ethernet, vs AC.

On the other side of things:

• With PoE you only have 1 AC-DC conversion happening, every wall wart power adapter has an idle power draw even without a load attached to it. With PoE you just have the single switch power supply wasting power.

Overall I doubt the difference will be large enough to matter, and some PoE switches are quite power hungry even with nothing plugged in for some reason, so could end up costing more.