...but, All-Star Comics came back in the 1970s, with All-Star Comics #58 (January-February, 1976), and it brought the Justice Society back with them, including new members, who started out first as the Super-Squad!
Seven Soldiers of Victory (and later revealed, the All-Star Squadron) all during World War II...and, thanks to a little time travel (and a JLA/JSA team-up), ended up coming out of the 1950s, to the current day.
Starting with the revived All-Star Comics, Star-Spangled Kid was using Starman's Cosmic Rod (on loan, as Starman had broken his leg), and got involved with helping the JSA save the world (along with the ex-Boy Wonder, Robin) and another new heroine, introduced at the time. The three formed a loose "super-squad", but then joined the JSA with All-Star Comics #64 (January-February, 1977), mostly to show off his new Cosmic Converter Belt, which was an improvement over the original, not only allowing Sylvester to fly, project beams and influence gravity, but also to change molecular structure (making things like Hawkman's wings, a spacesuit for Superman and other costume changes). Sylvester was also doing all this to impress his new teammate (with little success) and to help fellow Seven Soldier, the Shining Knight who happened by for a time.
Mighty Maid of Steel
married Lois Lane), so it took a little longer for Kara Zor-L to make her debut (that in All-Star Comics #58, January-February, 1976, by Gerry Conway, Ric Estrada and Wally Wood). Not quite as powerful as Superman, Power Girl was still leaping buildings in a single bound during her earlier appearances, but proved to be quite a help to the JSA as a part of the "Super Squad" with Robin and the Star-Spangled Kid, helping against Per Degaton and Brainwave, Vulcan and Zanadu before joining the JSA in All-Star Comics #64 (January-February, 1977, which also lured her cousin out of semi-retirement to help fight Vandal Savage).
Power Girl did quite well as a liberated new JSAer, working against the Injustice Society of the World, fighting the Underlord and his minions, and even helping the JSA against the Psycho-Pirate (who was turning JSAers against each other).
...(all of which says there is so much more to Power Girl, including her own regular series, so we'll look into more of her history later, as the various Crises and Justice Leagues come up!).
brief visit with "uncle Bruce" in Brave and the Bold #184, Crimelord from Wonder Woman #289 to #290, saving Alfred in Wonder Woman #294 and #295, fighting alongside possible Batman replacement, Blackwing against the Boa in Wonder Woman #296 to #299, fighting the Undertaker and the Mechanic over the course of Wonder Woman #301, villainous Pat Pending in Wonder Woman #302, and Dr. Tarr and Professor Fether through Wonder Woman #306, finding her own identity in Wonder Woman #307 and #308, meeting new villain Earthworm in Wonder Woman #309 to #313, more self-exploration in Wonder Woman #314 and #315, fighting the Sea Lion in Wonder Woman #316, the Nightingale in Wonder Woman #317 to #319, and finally finding herself in Wonder Woman #320 and #321.
Batman's daughter for a time), as well as putting the JSA in limbo for a time (all except Dr. Fate, the Spectre, Power Girl and the Star-Spangled Kid, and including non-members Hawkgirl and Sandy, partners of Hawkman and Sandman), starting with the Last Days of the Justice Society Special of 1986; this put the JSA on hold for a time, but you can't keep good heroes down!