OK. Understood.
Regarding RPi forum, if there is under-voltage issue, color (rainbow) square is displayed on the screen in right up corner.
Is this feature available in OSMC? If yes, when and how should I check for this square?
Edit: According to this topic it should be above clock on main screen of KODI - [solved] Flashing squares on the screen
I will check in details by changing screen resolution to make sure that it’s not there.
I heave read how to create own driver. Looks easier then investigate if power supply is powerful enough for RPi and WiFi adapter 