With USB Power Delivery, other supported Apple chargers can also be used to power the Apple iPad Pro besides the Apple 29W USB-C Power Adapter. One of these chargers is the Apple 61W USB-C Power Adapter that comes with the non Touch Bar version of the 13" MacBook Pro (Late 2016) and Touch Bar version of the Apple 13" MacBook Pro (Late 2016).
The Apple 61W USB-C Power Adapter later declares additional power profiles of 27 watts (9 volts @ 3 amps) and 60 watts (20 volts @ 3 amps).
The Apple iPad Pro again requests to be charged at 12 watts (5 volts @ 2.4 amps).
Although the Apple 29W USB-C Power Adapter provides the fastest charging to the Apple iPad Pro, it still gets a good charging experience with a USB Power Delivery based Apple charger like the Apple 61W USB-C Power Adapter.