I’ve been looking for components to run a Jetson Nano straight off of PoE, without a separate power supply.
The reason this can work, is that the Jetson has a pin header that breaks out the power-over-ethernet it may receive from the Ethernet port. You can then wire a DC DC converter to this PoE (which typically is 24V or 48V if you have PoE from your switch) and make it generate the 5V/10W or whatever that the Jetson wants (depending on your power mode and utilization.)
This product is $11.50 in single quantities, and tolerates all PoE voltages up to 53 Volts (which is 48 Volts plus 10%.)
It will, according to specifications, generate any power needed up to 3.5 Amps, which should be a Jetson running full tilt with a fan and some moderate power draw on the USB port.
If you know for sure that your PoE is 24V, or a very well regulated 48V that’s less than 50V, you could use a Pololu D36V50F5 buck converter:
(This product costs $20, and is made in the US, which may matter to certain government manufacturers, and people who prefer in-country support over the cheaper price from offshore components.)
You also need a simple diode bridge, because PoE doesn’t guarantee polarity, depending on wiring standard and cables used.
The wiring is pretty simple: Jetson motherboard header J38 -> diode bridge -> DC DC converter -> 5V and GND pins on the Jetson GPIO header J41.
Because you power it through the GPIO header, you don’t need to worry about the USB-versus-power-connector selector.
Hopefully this helps someone!