Unlike its predecessors, the new 2018 iPad Pro comes with a USB-C AC Adapter that supports USB Power Delivery (USB PD) fast charging at 18W. This wall charger can be identified by its model number A1695.
Another notable difference is in the included charge cable. The new 2018 iPad Pro ships with a USB-C to USB-C cable, whereas earlier iPad Pro models come with a standard Lightning to USB cable.
As of now, the 18W USB PD wall charger is not sold as a standalone product.