The four power levels
IEEE 802.3af (PoE) delivers up to 15.4 W per port at the switch. 802.3at (PoE+) delivers up to 30 W. 802.3bt adds Type 3 at up to 60 W and Type 4 at up to 90 W. The device receives a little less than the switch sends, because some power is lost in the cable.
What needs what
IP phones and many cameras run on 802.3af. Most Wi-Fi 6 access points need 802.3at for full performance, and some Wi-Fi 6E and Wi-Fi 7 models need 802.3bt. Pan-tilt-zoom cameras with heaters and small displays can also need bt. The device's datasheet lists its maximum draw and required class.
Port limit vs total budget
A switch can be PoE+ on every port and still not power every port at 30 W at once. The total PoE budget is the real limit. Add up your devices and compare. Our PoE budget calculator does this for you.