802.3af, 802.3at, and 802.3bt are the main official PoE standards and operate around 48V how much power (watts) they can delver varies. Some camera MFGs have adopted their own variant of at/bt that can deliver more power to a power hungry PTZ.
Passive PoE is not standardized, MFGs do whatever they want. It's cheaper / easier for them, at the expense of a few safety/quality features.
In case of the Ubiquiti NS-5AC-US it can be powered by a normal 802.3af switch at (48V) or Ubiquiti's 24V passive injector. This is uncommon. Often equipment designed for 24V passive PoE comes with a power injector you can use to supply power to the device.