My Apple USB-C to USB-C + 20W Brick Will Not Charge My iPad Pro 11", But WILL Charge ANYTHING ELSE USB-C

I would speculate that your USB-C Power Adapter may not be of Apple origin - but is instead a third-party Power Adapter.

Some third-party USB-C power adapters (and portable PowerBanks) do 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 your iPad and other Apple devices.

Proprietary charging standards such as QC (Quick Charge), often encountered with cheap(er) brands of Power Adapters, are not supported by Apple. When charging from a regular 5V USB power source, charging by your iPad is typically limited to ~12W (i.e., 2.4A @5V), regardless of the supply capabilities of the Power Adapter.

Many better quality third-party Power Adapters do support USB PD; check the specifications of your Power Adapter.

TopSecretMan wrote:

My USB-C to USB-C cable + 20W brick will not charge my iPad pro 11".

…

So what do I do?

Contact Apple Support.

Pick your country or region here: Contact Apple Support - Apple Support

I read somewhere that certified USB-C cables are supposed to be able to carry up to 15W of power safely, even if they do not support USB-C Power Delivery.

Cables that support Power Delivery must have embedded chips, to tell the attached devices that the cable can safely carry more than 15W. You could connect a USB-C device that could charge at up to 240W to.a USB-C power brick rated to delver up to 240W, and if the cable did not have the chips indicating that it could safely carry PD power, charging would fall back to a trickle (e.g., 5V/3A or less).

LotusPilot wrote:

I would speculate that your USB-C Power Adapter may not be of Apple origin - but is instead a third-party Power Adapter…

Or counterfeit.