From the manual:
When connecting the device to a USB 3.0/2.0 Type -A
port of the computer, you will need the included USB
cable and AC adaptor
How much power UR22C actually requires?
USB3.0 spec says that ports can deliver up to 900mA (Ports with charging capability, can provide more, usually between 2-3A, 1,5A by the spec),
so by the looks of it, it probably requires more than 900mA.
But manual does not say anything about 5V AC adaptor rating, which should be used with UR22c. 
My primary concern is, can it be Bus powered from regular USB3.0 port (900mA) or should I buy separate 5V adapter (not sure about the amperage as specification does not say anything about power draw).
So apparently no-one knows, even Steinberg reperesentatives… 
Fair enough, as I received my interface today, I will probably find out myself.
How it works? What is your impression of this audiointerface?
How it works? Great? What about headphones 250 Ohm?
UR44C has USB3.0 port. In the manual it is called USB 3.1 gen 1 port, which is the same as USB 3.0.
I have connected it to USB 3.0 port of the computer. If I choose USB power, the ring around Output knob keeps flashing and the interface does not work. After connecting the supplied 12v power cord and choosing it as power source the blinking stops and the interface works perfectly. (Win 10, Cubase)
So everything is cool. But as I formerly wrote, at least some basic EQ plugin for the output monitoring signal would make this kind of unit even better, as it gets used as a standard audio card also. A little software update perhaps?