I'm not really sure what you're asking. Are you talking about if you use a Wii instead of the SNES Classic for whatever your project is?
The wii2HDMI might not use *external* power, but it's still going to have power consumption of some sort. If you're worried about adding extra power bricks, that converter I linked uses 5v, the same as the SNES Classic. You could build an adapter to run them both off of USB, or have a USB power output on the converter box with relative ease.
If you're trying to build a portable with this, I don't know enough about either system to know what the best option is for you.