The other day while charging with my AC charger, I realized that charging port cap fits perfectly on the top of charger cap. Am I the only one who didn't know this or everybody does?
You're a bit late to the party but you're far from the only person still discovering this design feature.
This seems less a design feature and more a consequence of the fact that both the charging cable and charge port cover are the same size because they're both intended for a good fit in the same hole, therefore a cap intended for a good fit on one will also be a good fit for the other...
