There is a way to make RX420(RDP) and RX420(HDX), powered by Raspberry Pi4 platform, work with Power over Ethernet. An active PoE Splitter is required.  For example, below is the picture of a typical Active PoE Splitter, PoE to Raspberry Pi 4 compatible Adapter (5V USB-C Power + Gigabit Ethernet). With this adapter, you don’t need a separate power adapter to use RX420(RDP) or RX420(HDX). (Only for Raspberry Pi4. Not compatible with Pi 3B or 3B+ based RX model).

(Amazon retail price for the below solution is around $26)