Hi All,
I want to mention about a quick problem that i've encountered before, AR550 Router doesn't supply power to PD via GigEth PoE Port
1-) Check the device datasheets whether peer device supports same PoE standards 802.3 standards.
2-) Or you can run poe legacy command in the below in order to check the compatibility of the connected PD and don't forget the restart device !
AR550>system-view
AR550] interface gig0/0/3
AR550] poe legacy enable
AR550]quit
AR550>save
AR550> yes
3-) Check your AR Router power connections are correct

4-) If everything is okey for the previous checks,you can run the below commands and restart device
AR550>system-view
AR550] poe power-management auto slot 0
AR550] poe power-reserved 20
AR550]quit
AR550>save
AR550> yes
Have a nice day !