Was the name Adolf, a popular babies name in Germany directly after WW2?

Probably. There is no reason to condemn a fairly common name because of one bad actor. "John" remained popular in this country, even after John Wilkes Booth murdered President Lincoln. Benedict took a tumble in the U.S after the treason of Benedict Arnold.

For me, the strangest German names are Helmut, Wolfgang, and the like.

No, not at all, i believe it is against the law in germany to call your child adolf.

Not after, but probably was very popular in the period 1933-1938.

Maybe the first name Adolf decreased in popularity as a babies' first name because besides Hitler, another Nazi with the first name Adolf was SS official Adolf Eichmann.

There was no Germany between 1945 and 1990.

Only West Germany and East Germany.

Sure. The Germans were full of admiration for a war ciminal who just led them to an ignominious defeat and occupation by a foreign power.