Comic books and superpowers have been closely tied with one another since the first days of Timely and DC Comics, but nothing stays the same for very long. When he was first introduced, Superman couldn't fly, he was barely faster than a locomotive, and he had no issues with Kryptonite.
Much has changed in the intervening 80+ years, but the Man of Steel is hardly the only character to go through some changes. Mutants from the Marvel Universe are always having their powers tweaked and evolved with some making huge leaps in terms of overall destructive energy.
The times that superheroes gained new powers or had their powers evolve into something new are usually big deals in comics. Whenever a tried and true character's recipe is modified, fans take notice, because it's such a massive deviation from the norm.
It's almost always significant, mainly due to the fact they alter a character in a big way, or simply because something innovative was added to a familiar concept. It's a winning formula regardless, and with several Marvel heroes taking on new cosmic abilities for War of the Realms, there's no better time to look at the best occasions where heroes had a massive upgrade.
Superman's powers have gone through a lot of changes over the years, but it's rare that the Last Son of Krypton picks up something entirely new. That happened back in 2015's Superman #38 when Superman was given a new power by writer Geoff Johns in the form of a "Super Flare."
As any fan of the Man of Steel knows, he derives his powers from his unique Kryptonian physiology as it reacts to Earth's yellow sun. Over the years, the energy he absorbs enables him to do wondrous things, like shoot a heat ray from his eyes and lift massive objects.
That absorbed solar energy built up in his body for years, but as his new power revealed, he can release it all in one fell swoop. Doing so turns him into something of a walking nuclear bomb, given the amount of energy released is enough to destroy a small city.
When he uses the Super Flare, it's horribly destructive, but it has a downside. Expelling all of that stored energy at once weakens him to the point of being little more than a normal human being for about 24 hours. It takes a day to recharge and get him back to pre-Super Flare levels, but the power does come in handy in a pinch.