18W non PD charging on a USB-A port and that works fine as well even on the 20W charger. I'm not sure what google changed between the 4a and 5a, but I've noticed similar behavior. My guess is that my 20W charger
the movable reflective layer14is deformed and is forced against the optical stack16. A dielectric layer (not illustrated in this Figure) within the optical stack16may prevent shorting and control the separation distance between layers14and16, as illustrated by actuated pixel12bon the right in FIG...
moreI have the Pixel 6a, 5a and 4a. The 4a charges properly with every charger I have. The 5a and 6a don't charge properly with a 20W USB-PD charger I have, but charge fine with a 65W USB-PD charger from the same brand. These chargers are also able to do 18W non PD charging...