Q: Is it possible for the PowerPack 20K USB PD Backup Battery & Hub to fast charge both the iPad Pro 2018 and iPhone XS at the same time?
A: No, the PowerPack 20K only has one USB-C port. To fast charge both devices, you would need two USB-C ports each capable of 18W output.
The PowerPack 20K can only fast charge one device at a time. For the iPhone XS, you will need to use a USB-C to Lightning cable.