Though Adolph doesn't have quite the same cut off you might expect, it was falling rapidly long before the 30s and 40s. It looks like German names generally might have the same trend, try Otto or Franz for example.

It doesn't explain the "A"s either, Adolph was never ranked very high. It seems to be mostly down to the loss of popularity of Agnes, Albert, Alice, Anna and Arthur.

Wendy is another good example of the Kylie style trend, being as the name didn't exist until JM Barrie invented it.