Bates, Swan and Colletta conclude the Dr. Xadu story in Action 435 (May 1974).
Superman creates a giant tuning fork, and flies through it to create a sonic boom, and thus an earthquake. Only then does his awareness kick in, horrified at what he has done. Superman spends much of the story fighting against the destructive impulses that Dr. Xadu and Zeda send him.
Superman makes a lot of amazingly accurate guesses in this second half. He figures out that Dr. Xadu and Zeda are behind this, even though he did not recognize them last issue, and hasn’t seen them since his youth. He also deduces, from another painful bite of candy, that there is a transmitter on his tooth which sends his super-energy to the couple every time he struggles against their commands.
When Dr. Xadu and Zeda use their deadly power-grip on Superman, it’s hardly a surprise that he accurately guesses that a magnetically charged rock will take them down.
Dr. Xadu is relegated to comprehensive flashbacks for the rest of the decade, returning only shortly before Crisis on Infinite Earths, in the final issue of DC Comics Presents.