20 watt charging or not?

If you have any year iPad Pro with a 12.9 inch screen, you CAN use the 20W power/charging adapter block to PD fast charge your iPad Pro.

ALL year model iPad Pros DO fast charge with a larger wattage Apple power/charging adapter.

The ONLY iPad Pro model that may not fast charge is the 2016 9.7 inch screen iPad Pro.

I own two older 2015/2016, 12.9 inch screen iPad Pros and both fast charge with the Apple 20W power/charging adapter.

No problem. No worries.

Both of my iPad Pro models charge in less than 3 hours.

You will need to purchase a USB-C to Lightning cable, either from Apple or from better third parties on Amazon, like from Anker Electronics, Belkin Electronics or even from Amazon Basics cable products.

Best of Luck to You!

iPad has a huge battery, I think you can use 20W if you want to fast charge you iPad. But I recommend that you should not do that if you use iPad Pro 2018 or lower because it doesn't support that. You can see the model in Settings - General - About - Model Name