What you need is a PoE injector and splitter that will convert the DC PoE or PoE+ power to 24VAC power.
Here's a few that might help:
Tycon Power Active PoE Splitters AC & DC Output, will go up to 70W at 24VAC. Here are a few online suppliers.
Here is a diagram of how it works:
The 24VAC splitter goes near the camera. The high PoE or PoE+ injector near the network switch.
Vivotek 24VAC PoE injector/Splitter, I cannot tell the wattage from the web page and can't find that unit on Vivotek's site.
These units are not weather-proof, they will need to be installed in appropriate junction boxes if mounted outdoors.