Official Raspberry Pi Poe Hat

The Raspberry Pi Power over Ethernet HAT is a small accessory for the Raspberry Pi computer. The PoE HAT allows you to power your Raspberry Pi using Power over Ethernet–enabled networks; for this product to be used, the network it is connected to needs to have power-sourcing equipment installed. The PoE HAT is fitted with a small fan that is controlled by the Raspberry Pi via I2C.

Source: www.raspberrypi.org