How Well the Apple 10.5-inch iPad Pro Supports USB Power Delivery with the Non Apple Based Google Pixel 2's 18W USB-C Charger
Rather than 12W based charging that the Apple 10.5-inch iPad Pro originally gets from the Apple 12W USB Power Adapter, let's see if the iPad can charge faster using the Google 18W USB-C Power Adapter that came with the Google Pixel 2 and Google Pixel 2 XL phones. The Google 18W USB-C Power Adapter supports USB Power Delivery fast charging technology to offer up to 18 watts over USB Type-C in contrast to the Apple 12W USB Power Adapter which uses Apple's proprietary D+/D- based mechanism to provide 12W over a USB Type-A connector instead of USB Power Delivery.
To see how well the Google 18W USB-C Power Adapter charges the Apple 10.5-inch iPad Pro using USB Power Delivery, we find out using the GRL-USB-PD-A1 analyzer software from Granite River Labs. When connected over the Apple USB-C to Lightning Cable, the Google charger begins communication over USB Power Delivery by consistently advertising 15 watts (5 volts @ 3 amps) and 18 watts (9 volts @ 2 amps) power profiles while the iPad's battery is fully depleted.
A hard reset eventually occurs which is followed by the same power declaration by the Google 18W USB-C Power Adapter.
We can see at first the Apple 10.5-inch iPad Pro requests only 15 watts (5 volts @ 3 amps) from the Google charger which it then accepts.
The Apple 10.5-inch iPad Pro next follows up to request the max 18 watts (9 volts @ 2 amps) for fastest charging which it then goes on to establish this power contract with the Google 18W USB-C Power Adapter.
Later we also observe the same 15 watts (5 volts @ 3 amps) and 18 watts (9 volts @ 2 amps) power profiles being repeated by the Google charger as power delivery negotiation continues.
When first plugged in from zero charge, the Apple 10.5-inch iPad Pro when off initially pulls only about 1 amps current with the voltage starting at 5.1 volts. As power requests are made when reaching 2 minutes, both voltage and current levels increase to enable power to be drawn at around 18 watts (9 volts @ 2 amps). Over the next repeated power declaration by the charger and while the iPad is turned on or inactive, the voltage drops back down to about 5.1 volts and lower current is being pulled for charging to eventually happen at around 7.6 watts (5.1 volts @ 1.5 amps).
The Apple 10.5-inch iPad Pro is able to achieve close to 18W during power off which is higher than 12W charging from its own supplied Apple charger (more details here). When the iPad is on and asleep, most of the charging is at 7.6W which is similar to the USB Battery Charging 1.2 spec of 7.5W.
The Google 18W USB-C Power Adapter works fine to quickly charge the Apple 10.5-inch iPad Pro in power off state using USB Power Delivery.