After completing the power testing and while waiting for some USB-C adapter changers to facilitate some further testing, let's follow-up on LG comment in Insight into lan78xx driver support for Pi  about interface throughput.

 

Since I don't have a network analyzer to checks throughput, I did an internet search and came up with a software tool https://iperf.fr/  to make some measurements. From their website, iPerf3 is a tool for active measurements of the maximum achievable bandwidth on IP networks.

 

 

For the test, I made the Pi the host and ran the iperf3 command from my workstation connected to the network switch. The first sample data is throughput using the Microchip PoE and the second is just a 1 meter cable from the network switch direct to the Pi4B Ethernet connection. Two throughput tests were done.  First a 1 meter length of cable and then the max 100 meters.

 

As LG alluded to in his post, the Microchip PoE USB-C power device data throughput via the Pi4B USB-C OTG configured connector is significant reduced. The length of cable had no impact on the readings.

 

Pi4B OTG interface (1 meter cable)

Pi4B Ethernet interface (1 meter cable)

 

Pi4B OTG interface (100 meter cable)

Pi4B Ethernet interface (1 meter cable)

 

The Microchip PoE USB-C device is capable of providing a network connection but the Pi4B hardware limits the throughput.