48vdc is the standard, IEEE 802.3af-2003 provides for up to 12.95 W per port.
There are newer higher power standards and non standard voltage proprietary versions – the most common proprietary one is probably the Ubiquity WiFi ecosystem.
The Raspberry Pi POE Hat is interesting but expensive and you still have to run a UTP cable between it and the Pi, I just use Texas Wifi POE -> Ethernet and µUSB cable. Bulkier but a lot cheaper.