IPad Pro only charges with Nintendo Switch ac adapter..?

The hardware can fail.

I have an iPad mini 6, and it would no longer charge with any USB-A/USB-C cable. It would charge with a USB-C/USB-C cable and a USB-C power adapter. However, it wouldn't provide any data connection at all through any cable. I brought it to an Apple Store, they ran diagnostics (over Wi-Fi) and replicated the issue with the data connection. The port was also examined/cleaned and the problem persisted. It was still within the 1 year warranty and I ended up getting a replacement. This was from my work authorization and service receipt:

Problem Description/Diagnosis

Issue: Reports issue with USB-C port. 

Does not recognize on computer. Does not charge with a USB-A to USB-C cable. It used to do both. 

Steps to Reproduce: Verified issue persists. 

Cleaned port, issue persists. 

Charges normally with a USB-C cable and power adapter. Charges when connected to Mac. Does not recognize on KGB computer. 

Cosmetic Condition: Did not personally observe visible signs of external damage that would prevent service. Did not observe damage to pins. 

Proposed Resolution: Replace under limited warranty at no cost to customer.

If it's out of warranty, then that might be a little bit trickier. Apple doesn't provide fixes to a customer's hardware. It's all through exchanges at a single price point unless it's as a battery service.

These support pages should help with troubleshooting battery and charging issues:

Charge and monitor the iPad battery - Apple Support

If your iPad won't charge – Apple Support

Troubleshooting generally requires substitution of the Power Adapter and cable for another known-good item. Most models of iPad require a Power Adapter rated at 12W or greater to reliably charge. 5W Power Adapters intended for older models of iPhone are inadequate to charge an iPad; if the iPad charges at all, charging will be very slow. Most (if not all) recent models of iPad are now supplied with a 20W USB-C Power Adapter that supports USB PD (Power Delivery).

Be aware that many computer USB ports cannot source sufficient power to charge an iPad. Unless explicitly designed for charging connected devices, computer USB ports are typically limited to 0.5-1A @5V (i.e., 2.5-5.0W). You should also be aware that while most Apple devices support USB PD, they do not support other proprietary or fast charging standards - such as QC (Quick Charge).

If you continue to experience difficulties when using an appropriate Power Adapter of 12W or greater, you might be best advised to seek assistance directly from from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively, if you have access to another Apple device, 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, Power Adapter and cable(s):

Genius Bar Reservation and Apple Support Options - Apple