PoE means Power over Ethernet. One Cat 6 cable carries data and power. A PoE switch is the box that feeds that power out of each port.
Plug the camera, door station, or access point into a PoE port. Plug the switch into regular wall power. The device at the far end does not need its own power brick.
The recorder (NVR) often has PoE ports too. Those ports are for cameras. A separate PoE switch is for extra cameras, door stations, access points, and anything that will not fit on the recorder.
Use a real PoE switch from this shop. A cheap no-name switch is how cameras drop offline.
Shop PoE switches · When you need a switch
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