@mg666 

Hi

When the Powerline adapter is successfully configured, whether it is connected to a router or a Powerline adapter, the IP of the device is assigned by the router, so the printer and other devices can communicate with each other.

To check the connection between computer and Printer,try to ping printer IP address from computer and see if that is accessible.
How to Use the Ping Command
How to find IP address on your devices?

  @Joseph-TP hi, thanks for reply. Of course I use the ping tool. Whenever the printer connects to the wifi of the adapter, it is not possible to ping it from the original routrt wifi. It is possible only when connecting to the same network of the adapter. 

Is this wifi adapter working in truly access point mode? There are almost no settings in web interface of the adapter but I see there are settings for the subnet mask there, so isn't this adapter creating some sort of sub-network which makes devices connected to it not visible from the original router network? 

It looks like you blocked possibility of pasting links here, but on ubiquiti forum there was one topic with very similar problems. Someone had two wifi access points, one was connected to the main router through tp link extenders and he had problems with devices visibility when the user was roaming between the two access points - in my case there are also two access points to the same wifi network in fact - one is the main router and the second one is the wifi power line adapter. Last post with solution stated that it was the fault of the adapters because multicast traffic wasn't forwarded correctly and switching to different adapter vendor solved the problem. There the problem was not even with WiFi adapter but with the basic PA4010... 

  @mg666 

Hi,

It could be that the signal quality of the Powerline connection is marginal.

To rule out that this is the case temporarily plug the WPA4220 adapter into a wall socket that is no more than a couple of meters away from the PA4010 and then perform your ping tests again.