The Ethernet LAN connection can provide power to a device so that it doesn’t need a local power source. Devices such as IP Phones, Wireless Access Points, IP Gateways, PDAs, etc. often look to receive power over the network cable attached to them. Switches usually have an internal setting that limits the amount of power it will deliver to devices connected to it. It must be understood that power for a device is not routed over multiple hops; it is the last hop device that supplies that power.
Switches have an absolute power rating when it comes to supplying power to devices. Often that maximum power available to power devices connected to a switch’s port is under 500W, with individual ports allowed to deliver only a fraction of that, usually under 20W. You can usually set a limit under that amount if you are worried about heat, power supply load and their effects on reliability. Any devices added to a port that exceed these settings simply will not be powered.
An IP camera or wireless access point requests ~25W (PoE+), but the switch port only provides 15.4W (standard PoE), resulting in a mismatch.
show power inlineinterface Gi1/0/1 power inline autoshow logging