Based on the ideas thread it isn't obvious that chunk size means "per byte".  I suggest either specifying the number of base digits per delimiter.  Or using a name other than chunk that indicates it means bytes.

If we're going to do this, it should also be done for octal formatting (the 'o' code) for consistency.

Also, per the python-ideas thread, via parameters to the .hex() method on bytes/bytearray/memoryview.

I'm inclined to leave 'A' printable-ascii formatting out.  Or at least consider that it could also work on unicode str.