Super Intelligence: Your setting has a misanthropic scientist who is so far above and beyond normal that he has in a single lifetime gotten too far ahead of modern science for people to understand what he is doing, and he has no inclination of explaining what all those middle steps are. This is generally my least favorite approach since it often ignores the HUGE infrastructure that advanced technology actually requires and creates a terrible return on investment compared to mass produced gadgets. Tony Stark & Bruce Wayne are the only 2 examples of this trope being well executed that I can think of because they were both super intelligent AND hadenough to invent things that were hard to reverse engineer, had access to multi-billion dollar military tech R&D facilities, but saying you needand most importantly, they both ultimately decided they did not want to sell their weapons technology for ethical reasons. That said, needing to have a private arms company in your back pocket that you spontaneously decide not to be a superherouse significantly limits the number of heroes and villains your setting can have.
If I were to incorporate this trope as the baseline for all supers in my world, I would have the inventor create a bunch of prototypes as he tries to figure out what production model he will go with, then kill the scientist preventing his work from ever reaching the industrialization stage. Then you scatter to prototypes as needed to fit your plot.
Time Travel: Your heroes and villains are from the future, fighting with what to them is just normal technology. If the current era is ground zero for a temporal war between future civilizations, then much larger numbers of heroes and villains may come into play, but it means that your powers are likely to be standardized kits rather than unique powers. If a single organization sends back 10 herosheroes, chances are they will all have the more-or-less the same general kits and therefore similar power sets.
Here the future people want to control the narrative of history which they can't do by just giving thier tech away willy nilly; so, they control its distribution very tightly.
Alien Technology: This is my personal favorite because technology falling from the sky can land in anyone's backyard. Since any rando can come across it, you can have an environment similar to Central City of ordinary people being elevated to hero/villain status instead vs everything being accumulated in the laps of the powers that be. Also This also means no one on Earth actually knows how it works to even try to mass produce it. Lastly, something like an alien ship exploding leaving tech all over the place to be found is going to give you a much more diverse set of powers since the debris form the ship's medical lab will be different than from the arms locker which will be different from the machine shop, etc.