What is the purpose of the circular cutouts on the charger cap?

To keep the cap somewhat attached on the cord, so it is not dangling while plugged-in. Not sure if that was what it was for, but that's how I used it.

 

Hang the cap on the cord.

Keeps it from flapping around and dinging the paint on a windy day.

 

Kinda like the holder for the gas tank cap. That gas tank cap is a pain on windy days when filling up unless it's in it's holder..... And that OEM EVSEs cap dongle / attaching cord is just as much of a pain to untwist when it gets all wound up.

 

And I see you also put the cap in the place holder for what would have been the fast charging port in Japan.