A small number of reports have been seen within the Apple Support Communities of the issue that you describe - which might suggest a software update issue, or a problem with a small number of devices. Placed in context, given the millions of devices in use globally, this not a widespread issue.
Your USB-C Power Adapter and iPad use USB PD (Power Delivery) mutually negotiate the charging profile (i.e, voltage and current) used to charge the iPad. This process is both hardware and software dependent; if the negotiation fails, the iPad may not charge.
Connecting your iPad to a computer (or using a Power Adapter with the older USB Type-A connection) removes USB PD from the charging equation - charging the iPad at the standard USB 5V, albeit limited to a reduced 12W charging rate.
As described, your iPad will charge from a UDB 5V power source, but not from a USB-C source that used USB PD. This suggests either a software issue, or a hardware failure that impacts charging.
You may have already attempted some of the following...
Begin with a forced-restart of your iPad - as this will often clear an isolated software issue:
Force restart iPad (models with Face ID or with Touch ID in the top button)
If your iPad doesn’t have the Home button, do the following:
- Press and quickly release the volume button nearest to the top button.
- Press and quickly release the volume button farthest from the top button.
- Press and hold the top button.
- When the Apple logo appears, release the top button.
Force restart iPad (models with the Home button)
Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
If the problem persists after performing the restart, it may be necessary to reset your iPad settings. While this reset will not cause any loss of data, as a precaution, it is always wise to ensure that you have a current iCloud or iTunes backup before performing the reset:
How to back up your iPhone, iPad, and iPod touch - Apple Support
When you are happy to proceed, you can perform the reset from iPad settings:
Settings > General > Transfer or Reset iPad > Reset > Reset All Settings
If the problem still doesn’t clear, the next step is to reset the iPad to factory settings:
Restore your iPhone, iPad, or iPod to factory settings - Apple Support
Otherwise, you would be best advised to seek assistance directly from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively and perhaps easier, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:
https://apps.apple.com/app/apple-support/id1130498044
You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad - and you can explore your available options:
Genius Bar Reservation and Apple Support Options - Apple
