Best Adaptor for IPad Pro 12.9 (first gen)?

Quick, simple answer, yes!

On a 1st gen iPad Pro, you can even use the new 18W USB 3.0 Apple power adapter with an Apple USB 3.0 to Lightning cable to charge your iPad little faster.

I started using this setup since the beginning of this year.

Also, charging will go faster if you charge while not using your iPad and you disable WiFi and Bluetooth while charging.

My 2015/2016 12.9 inch screen iPad Pro charges from 5% to 80-85% in a about 2 hours, or so, when WiFi and Bluetooth are both turned OFF and I just let the iPad sit and charge.

My iPad charges to 100% in a about 3 hours, or so, using this procedure with the 18W adapter.

Best of Luck to You!

its ok

all chargers provide 5volts

that mean unless it's an unofficial charger which for whatever reason provide higher

it can never harm your ios device (unless an unofficial connector is shaped in a way that fracture your charger in your ios device)

ipads however charge with a higher amount of amps than iphones so if iphone ac chargers are used it charge very slowly

if one connect a charger which is able to provide say 120000Watt the ios device will not charge more than it would build to charge

so as long as it's 5volts everything is safe