Your car's USB Type-A charging outlet will provide "standard" USB 5V charging - potentially limited to 10-12W (i.e., 2.0-2.4A @5V). By contrast, your iPad's USB-C port, when connected to a compatible USB-C Power Adapter, uses USB PD (Power Delivery) protocol to negotiate a mutually power profile to use for charging - this using a higher charging voltage.
USB PD is an active protocol reliant upon both hardware support and software. The Power Adapter, connected device and charging USB-C cable (the cable itself incorporating active electronics) all participate in the negotiation protocol.
As described, these are the likely sources of issues:
- Your iPad's internal charge controller has failed - but can still charge your iPad when using a standard USB Type-A power source capable of ~12W @5V.
- Your USB-C Power Adapter either does not support USB PD, or itself has a fault.
- Your USB-C charging cable has a fault.
Assuming that the charging problem is not mechanical (i.e.,damaged or dirty USB-C port), 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 (i.e., 2.4A @5V) or greater to reliably charge. 5W Power Adapters (1.0A @5V) intended for older models of iPhone are inadequate to charge an iPad; if the iPad charges at all, charging will be very slow. With the notable exception of EU Member States, many recent models of iPad are supplied with an Apple 20W USB-C Power Adapter.
Some third-party USB-C power adapters (and portable PowerBanks) may not support USB PD (Power Delivery). Power Delivery mutually negotiates the charging voltage; the source, load and cable are all elements involved in the negotiation protocol. Unless the Power Adapter explicitly supports USB PD, it will almost certainly fail to charge the iPad; proprietary charging standards, such as QC (Quick Charge), are not supported.
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, you can initiate and manage your support cases from Apple devices using the excellent Apple Support App. If not already installed, 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
