Shazam! 6 (Oct 73) has a cover that is both a photo cover, and an infinite cover, making this a desirable issue for collectors of such things.
And that's good, because there is little else worthy of making this issue collectable. O'Neil and Beck do the lead story, which brings back Sivana. He makes a watch out of suspendium, gets into a disguise, and gives it to Billy Batson as a gift.
The effect of the watch is to cause Billy to lose two minutes of time whenever he says Shazam. He freezes, not experiencing the missing time. I like the re-use of the suspendium, but Sivana never really takes any advantage of the situation he has caused.
Billy never really notices what is going on, but does see that his watch is running slow. He winds it a few minutes ahead, and this somehow ruins the suspendium, so the next time he says Shazam the watch just explodes, and Captain Marvel is free to catch Sivana.
Maggin and Beck do the back-up story, which brings back Dexter Knox, Billy's whiz kid scientist friend.
Knox builds a machine that can create huge amounts of electrical power, and his grandmother unwittingly charges herself from it. This causes her no pain or anything, but she is carrying a destructively huge charge, enough to power an entire city.
Lucky for them Miami suffers a blackout. Captain Marvel flies Dexter and his grandmother down there, and she powers up the city.