PoE power sourcing equipment (PSE)

PoE delivers DC electrical power over Ethernet cables to connected network devices. The device delivering the power is called the Power Sourcing Equipment or PSE.

PSEs can come in various forms. The most common, convenient, and preferable is in the form of a PoE enabled switch that delivers both network connectivity and PoE to a PD. Other than a PoE switch, PSEs also take the form of:

• Midspan - An intermediate device between a non-PoE switch and a PD that delivers power to the PD. Midspans typically have the same number of ports as the non-PoE switch that it connects to, although this is not strictly necessary.
• PoE injector - A device that "injects" power into an Ethernet connection. It works much the same way as a midspan, but delivers power to a single device.

Both of the above devices plug in to mains power and have a transformer that enables them to deliver power to the PD.

Typically, PoE switches will conform to some standards-based PoE, or "Active" PoE. Most PoE injectors will usually use passive PoE although you may find standards-based injectors as well. Both active and passive PoE midspans are generally available.

Links:

https://networklessons.com/cisco/ccna-200-301/power-over-ethernet-poe