In any PoE environment there are two types of devices: PSE (Power Sourcing Equipment), and PD (Powered Device). Power over Ethernet (PoE) standards define the maximum power levels that can be delivered over Ethernet cables, and each standard has a PSE standard and a PD standard.
IEEE 802.3af (PoE):
Delivers up to 15.4 watts of power by the PSE.
12.95 watts of power available to the PD.
Suitable for low-power devices like IP phones, some cameras, and wireless access points.
IEEE 802.3at (PoE+):
Also known as PoE+ or PoE Plus.
Delivers up to 30 watts of power by the PSE.
25.50 Watts of power available to the PD.
Suitable for devices that require more power, such as thin clients, network switches, outdoor access points, and surveillance equipment.
IEEE 802.3bt (4-Pair PoE or PoE++):
Also known as PoE++ or 4-Pair PoE.
Two classes:
Type 3 (60W): Delivers up to 52 watts of power to the PD.
Type 4 (99.9W): Delivers up to 71.3 watts of power to the PD.
Suitable for high-power devices like PTZ cameras, laptops, and small appliances.