Wait, before we get too deep into this, what case are you actually planning to use? Like, the clearance difference between a 10L and a 20L case makes a massive difference for ur cable management and budget. Also, what kind of hardware are we talking about powering? Honestly, SFF builds can get wayyyy expensive if you aren't careful, so here is some advice from someone who has built too many of these things: * Stick with brands like Corsair or maybe Cooler Master. Basically, just get any modular SFX unit from a big name and you'll be fine.
* Don't overspend on Platinum or Titanium ratings if ur on a budget. A Gold unit is reallyyy the sweet spot for value and you won't notice the difference in a typical build.
* Make sure whatever you get is fully modular. Dealing with extra fixed cables in a tiny case is basically impossible, trust me on that one lol. But yeah, give us those case specs and your budget so we can actually point you in the right direction!

For SFF builds, high-quality SFX PSUs are generally recommended for their optimal size. However, some SFX-L units offer slightly more wattage. Prioritize 80+ Gold or Platinum for efficiency and check compatibility with your case's airflow.