Finally, if you have a MacBook Pro with an Expresscard 34 slot, you could get a FLUSH USB 3.0 card and add a port that way.
Even after all this, you may still find that you won't get 15W out of the port. Many USB ports on laptops limit them selves to 500mA. Or they won't go higher without being plugged in, things like that.
This seems so throw back but perhaps try finding a USB 3.0 Expresscard. Something like this (which is the model I got for the ol' T410 I own since 2010): https://www.amazon.com/dp/B00BB7TVMO
I have this one https://www.amazon.com/gp/product/B00BB7TVMO/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
And it works fine on my T420 under debian.