The PWR-Line is a replacement power adapter for the MikroTik microUSB router. It is compatible with all the latest microUSB devices powered by MikroTik, a simple software upgrade to v6.44+ enables this feature (supported by the listed devices with serial numbers ending in /9xx. The PWR-LINE feature is also supported by some previously manufactured devices - if you have a device with a serial number ending in /8xx, upgrade to 6.44 and see if the PWR-LINE interface appears).
Simply remove the old microUSB power adapter and replace it with the PWR-Line adapter. The device is still powered by USB, but now gains a new Ethernet interface, which works through the electrical network. Connect another PWR-Line device somewhere in your apartment, and the devices will join together, allowing you to extend wireless coverage or simply facilitate connectivity between different rooms, without the need to lay any wiring.