Having now zapped the ethernet circuits on two w32-eth01s when powering via a PoE adaptor, I found the following info from
Olimex, which also applies to these cheaper devices:
Important notice: ESP32-POE has no galvano isolation from Ethernet's power supply, when you program the board via the micro USB connector the Ethernet cable should be disconnected (if you have power over the Ethernet cable)! Consider using Olimex USB-ISO to protect your computer and board from accidental short circuit. Also consider instead using Olimex ESP32-PoE-ISO board which is insulated.
I was connecting a pc to monitor the esp serial output via a USB adaptor while powered up via a PoE adaptor; the spike caused by hooking the pc ground to the floating device "gnd" connection killed the ethernet circuits. They still work on wifi, though.
