Part 5 of "The Colors Out of Space"

Kryptonite-Plus. Action #350 tells the tale of The Heroes, a musical group that plays dressed as Green Arrow, Green Lantern, Batman, and Supergirl. But they do more than sing: During breaks at their gigs, they steal from their hosts, nabbing such things as "Carter Hagen's valuable mineral collection." When Supergirl tumbles to their racket and busts in, the fake Green Arrow pulls out some "Kryptonite-Plus from the mineral collection we stole. It's a super-powerful isotope of Kryptonite that will finish her off in minutes!" Need I explain that the Maid of Steel escapes?

Jimmy Olsen #126's cover story featured "The Riddle of Kryptonite Plus," not hyphenated. However, there really ain't no such animal. Jimmy, on the moon with another astronaut, comes across Superman's body sprawled on a pile of multi-colored rocks which Jimmy assumes are "some sort of ultra-Kryptonite." But it's all a scam, part of an elaborate, though doomed, deception by a group of super-powered aliens trying to invade Earth. And that's the last we hear of Kryptonite Plus, with or without a hyphen.

Anti-Kryptonite. When those nasty old Vrangs landed on the floating charnel house that once was Argo City, before their encounter with Jewel Kryptonite as described above, they didn't reckon that they were standing on the universe's only known specimen of Anti-Kryptonite.
Anti-K came about, I suspect, to cover another of those sloppy continuity errors I mentioned earlier.
Y'see, in Action #309 Supergirl learns about the Argo City religious nut, Jer-Em. As we al know (or should know), the soil of Argo City became Green Kryptonite in Krypton's explosion; only Zor-El's handy-dandy stockpile of lead sheeting saved its citizens. Later on, as we learn in this issue of Action, Argo city drifted into a yellow-sun system like our own, thus giving everyone super-powers. Then Jer-Em is alarmed and proclaims, "The Gods of Krypton would have given you wings if you were meant to fly!" (I am not making this up, I promise!)
Then, using his own powers, he flies (!) out of the protective dome and below the protective lead. Putting his hands on the bare Kryptonite rock, he super-shoves Argo City back towards its red sun before boogying back inside. Then, for the "crime" of taking away their super-powers, the frustrated Argo Citizens zap Jer-Em into the Phantom Zone. This was in Action #309.
Well sir, in Action #317 a sharp-witted reader wrote in to ask how Jer-Em had survived that long exposure to the Kryptonite below Argo City. The response? "Obviously, this was a freak type of Anti-Kryptonite which affected only non-super Kryptonians."
Oh. Obviously.
Anyway, Action #371 reiterates this doctrine, when recounting the death of Morina, Kara's childhood friend: "That Anti-Kryptonite, which could kill Kryptonians without super-powers, was to destroy all life in Argo City some years later!"