It would be the part that would plug into the wall. The usb usually plugs into the actual plug, if that makes sense.. ha funny how I work at a technology company and still can't figure out the proper terminology for all this!
Both, as long as they have the USB.. I think you can charge anything up to the size of the iPad, I think a computer (for example) would probably require to much power, I should have mentioned that above.
It wouldn't be the same size as what your iPhone plug is, it is the same shape as a zip drive, you would have to have a USB cord to plug it into the power bank. Kind of like the ports you have on your computer when you plug your phone in to upload music. Hope that helps! It's in the box so I don't want to remove it..