Why is my iPad Pro (11inch) only charging with a specific 20W Anker USB-C adapter?

Contrary to what you may read elsewhere, there are indeed considerations for the Power Adapter used to charge Apple devices. Power Adapters are by no means universal - in particular USB-C Power Adapters which may not support USB PD (Power Delivery) - and may instead use a different proprietary charging standard. I'll cover this in more detail shortly.

Verify that your charging cable is in good condition and properly connected to both the Power Adapter and iPad. If the charging cable won’t properly seat or easily fit into the charging port of the iPad, this might indicate that either dirt or lint is obstructing the plug, or the plug or charging socket have been damaged. A damaged charging cable must be replaced - whereas a damaged charging port must be repaired. If experiencing difficulties with charging, using an Apple-branded cable (such as that supplied with your iPad) will help with troubleshooting - as this will definitely be USB-C Certified and be the correct specification.

If the problem is due to a visible obstruction, you may be able to remove it yourself*. With good light, using a sharpened wooden matchstick or plastic toothpick, very gently try to dislodge a visible the obstruction from the socket. Be careful to avoid damaging the delicate electrical contacts within the socket. Note that a USB-C socket has an obvious "tongue" within the socket.

(*) Removal of an obstruction is often best entrusted to the technicians at the Genius Bar of your local Apple Store or Apple Authorised Service Provider (AASP) - where the appropriate tools and expertise are available:

Genius Bar Reservation and Apple Support Options - Apple

If the charging problem is not mechanical, 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.

NB: Many recent models of iPad are supplied with a 20W USB-C Power Adapter - although in the UK and EU, a Power Adapter is an additional purchase as it is not included with the iPad/iPhone.

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.

Many computer USB ports also 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).

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

When using a USB Type-A Power Adapter, your iPad will always be charging using the basic 5V USB supply - which, for iPad, is limited to 5V @2.4A (12W).

By contrast, when using a USB-C Power Adapter that supports USB PD (Power Delivery), the iPad and Power Adapter will actively "negotiate" a power-profile that will use a higher charging voltage (5/9/12V or greater) - that allows for higher power without increasing the charging current (that must be limited to protect both the cable and charge-controller of the device being charged).

If your iPad can be successfully charged from a USB Type-A power source, but not from a USB-C/USB PD, this suggests failure of the iPad's charge-controller hardware or associated software issue.

Performing a factory restore of your iPad will reinstall a fresh copy of the most recent version of iPadOS supported by your iPad - which may resolve the problem with the iPad's charge-controller. If not, this would almost certainly confirm hardware failure of the charge controller chip - requiring repair to resolve:

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

Otherwise, you would be best advised to seek assistance directly from Apple Support - and request a remote diagnostic test. 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

For practical purposes, in lieu of repairing and returning your own iPad, Apple usually exchange the iPad for a renewed/refurbished iPad of the same model and specification. The cost of the exchange is the same as would otherwise be charged for repair. Unless you have benefit of an active AppleCare plan, an out-of-warranty repair while expensive will be somewhat less than the cost of a replacement iPad.

As for out-of-warranty repair costs, Apple offers a fixed-price price repair. You can verify eligibility and cost for your region/country here:

iPad Repair & Service - Apple Support

If you have an active AppleCare+ plan, the cost of repair is reduced to a small excess/deductible fee.

Never heard of an iPad having issues with certain chargers. I would check to make sure there isn't anything in the usb-c port on the iPad. Also, you mentioned trying different chargers have you tried different usb-c cables? Do you have an apple store nearby? Take it in for a diagnostic and see what they say. Also, is your battery health above 80%.

Hope this helps.

Paul

A charger is all it is. An iPad doesn’t care where it gets it electricity. More than likely it a charging cable issue.