Q: pencil does not charge when connected to cable

I only use cables I purchased through Apple or that came with my apple products.  I've tried different cords, even the one that came with my ipad pro 9.7 and the pencil only charges when attached to the pro lightening adapter port.

I Must be missing something then, because even on the apple website it says you can use the adapter the pencil came with to charge the pencil with the usb cord.  It just won't charge as fast.  I mean I'm ok with connecting it to the lightening USB port on the iPad cuz it does charge fast, but I just like the option of using a cable if needed and wanted to make sure it works that way, since it says it is suppose to.  Thanks for your time.

https://support.apple.com/en-us/HT205236

in that link after drawing, it talks about charging the pencil, has pictures too.