The Yamaha/Steinberg UR22C audio interface just came out in 2019, so I haven’t seen detailed information on it, aside from what’s in the manual.
I did some research, and the UR22C can be powered the following 3 ways on Macbook Pros:
- using the included cable on Apple Macbook Pros using USB 2.0 (tested on “early 2011” MBP. “System Report … USB … Yamaha UR22C” says “Power Available: 500 mA and Power Required: 500 mA”)
- newer Apple Macbook Pros that support USB 3.0
- external 5 volt/500 (or more) milliamp mini-USB adapter (mentioned in the UR22C manual, but the adapter is not included, and not tested by me) – nobody has heard of an official adapter, so you very likely don’t need this.
The list above should also be a good starting point for Windows or Linux.
Another thing to know is that Mac OSX supports “aggregated MIDI interfaces”, so if you have an existing audio interface like a 22 and buy another 22, you can combine them into a 44 using the Mac OSX “Audio MIDI Setup” utility. 
steinberg.net: Steinberg UR22C Manual
support.apple.com: If a Mac accessory needs more power or is using too much power