One indicator I’ve used is the UL number of a power supply. UL actually certifies that a product is "safe" to use within a determined operating range and environment. Although I don't believe they actually load test every power supply, cross referencing a UL number can be handy for many reasons.
You can use a UL number to find out who actually makes a particular power supply. Also, if the UL logo is on the same label as the specs, you can be pretty sure that the UL listing pertains to the specs on that very label. Can you believe that there are a few companies that claim UL listing, but don’t put the logo on their label? That’s because the specs on that label are not the specs given to UL. And it’s a regular Easter egg hunt trying to figure out what the actual specs are using the UL number. So why bother? If the company can’t put a UL logo on the same label as the specs, they have something to hide and not worth doing business with.
It used to be that one could classify the quality of a power supply is just from its weight. Unfortunately, as power supply topolgies change and newer, more efficient designs are introduced, better power supplies become lighter while an old, antiquated design may still be heavy.
Also keep in mind the “get what you pay for” adage. It doesn’t always apply from brand to brand, especially if people take into consideration USEFUL improvements like modular cables, active PFC, etc. all add to the cost of a power supply. But when you see a power supply with a bunch of lights and other pretty things, you have to take into consideration that this added bling isn’t free.