You can’t.

Even quality brands have crappy models.

They are not necessarily the cheapest ones, it is possible that the 400w is fine, the 550w is crap, and the 600w is fine again, even if they are in the same series.

They can also change the specs over time, without any indication on the packaging.

You have to look for reviews where they actually disassemble and check the insides of the psu to determine if it is a good buy.

There is a forum local to my language where they keep track of the small number of truly recommended models, there must be an English equivalent.

The 80plus sticker program doesn't mean a lot, but it does mean a little. Being from a brand that's been around for a long time and is not known for cutting all the corners helps too.