Hi I'm using OpenWrt 19.07.5, r11257-5090152ae3 on the mikrotik router.
After I fried the second usb ethernet adapter I noticed that I was connected to port 5 of the router which is the poe out port. So I measured the pins on the plug and noticed i have 9V on a couple of them.
So I assume that this is destroying the adapters.
When I check the gpios I notice that one is responsible for poe, at least that is what I'm thinking
oot@mikrotik:~# cat /sys/kernel/debug/gpio
gpiochip0: GPIOs 0-31, parent: platform/ath79-gpio, ath79-gpio:
gpio-3 ( |POE power ) out lo
gpio-12 ( |rb:green:user ) out lo
gpio-13 ( |USB power off ) out hi
gpio-20 ( |Reset button ) in hi
gpiochip1: GPIOs 488-511, ath9k-phy1:
gpio-489 ( |ath9k-phy1 ) in lo
So I changed its value
oot@mikrotik:~# ls -ahl /sys/class/gpio/gpio3/
drwxr-xr-x 2 root root 0 Jan 1 1970 .
drwxr-xr-x 4 root root 0 Jan 1 1970 ..
-rw-r--r-- 1 root root 4.0K Feb 16 20:52 active_low
lrwxrwxrwx 1 root root 0 Feb 16 20:52 device -> ../../../gpiochip0
lrwxrwxrwx 1 root root 0 Feb 16 20:52 subsystem -> ../../../../../../class/gpio
-rw-r--r-- 1 root root 4.0K Feb 16 20:52 uevent
-rw-r--r-- 1 root root 4.0K Feb 16 20:52 value
root@mikrotik:~# cat /sys/class/gpio/gpio3/value
0
root@mikrotik:~# echo 1 > /sys/class/gpio/gpio3/value
root@mikrotik:~# cat /sys/class/gpio/gpio3/value
1
root@mikrotik:~# echo 0 > /sys/class/gpio/gpio3/value
It seems to be low active so I first changed it to 1 which only led to to the pins being on 24 V 
Changing it back to 0 leads to 9 Volt.
Am I missing something here or do I have to disable this somehow differently. The mikrotik documentation tells me its passive poe.
Can I somehow disable this?
Any suggestions?
Thanks guys