TLDR: The 45W charger was faster in both the iPad Pro’s built in port, as well as the one in the Magic Keyboard’s hinge, but you lose about 25% of the speed when using the Magic Keyboard’s port. Both ports are still faster than the stock 18W charger, though.
Finally, a more interesting chart! While I found no difference between charging the 12.9” iPad Pro through the iPad directly or via the plug in the Magic Keyboard, that initial test was only using the stock 18W charger that comes in the box. The iPad Pro can charger faster than that, so I wanted to find the limit on how fast the new Magic Keyboard USB-C port could go if given more power.
After thinking I didn’t have anything more powerful at hand, I realized my wife’s laptop (a Dell XPS something-or-other) had a perfectly capable 45W charger I could use, so I was back into Fortnite to try and kill my battery a few times to get some readings.
Again, these were two hour charges using a 45W charger from Dell. The results?
Well, as you can see from the graph above, the gray line, which was using the higher watt charger in the Magic Keyboard’s port, resulted in marginally faster charging than the previous tests with the 18W charger. The real difference is when you see how it fared using the iPad’s built in port, which was about 25% faster than using the keyboard’s port. It was so much better that it hit 100% before the end of the test, which is fantastic.