Not only does this charge my Pixel 2 at the max 15 watts, but it also charged my 15" Retina Macbook Pro *while I was using it*. I was super impressed.
I assume it must have been putting out the max 27W, and I connected it to the computer with #27907 which is a 5A USB-C cable. At first the computer's battery menu said "not charging" and it was slowly losing charge (i.e. the power input was being supplemented by the battery). I closed a couple Chrome tabs that were taking 100% CPU, and with low CPU usage I saw the battery gauge actually tick upwards slowly. Not as fast as Apple's wall charger of course but great for riding down the road.