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

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