Ever bought the cheap $2 flip-flops from a local Dollar store? How long do they last? One walk on the beach, one walk down a flight of stairs before the front toe-thong rips out and you trip? Can you ever trust that that toe-thong won't rip out at any given moment?
Then compare that to a decent pair of Adidas or Nike sandals. Built heavier, more durable, you can even run in them.
That's the difference. Trust. Materials. Usage.
Quality psus not only have the right protective circuitry, it's also set right, to meet ATX standards. Many cheaper models might have the circuitry, but use cheaper and less reliable components. A good quality OPP protection will shut down at @ 120% over-power, cheap units won't, may not shutdown until 140%+. Cheaper units say they have OCP, but on reaching amperage limits, keep on going, possibly causing irreparable damage. OVP? A psu is supposed to be 12v (11.9v-12.2v). What happens when a psu dumps out over 13v? Poor VRM's get cooked. Cheap units might not trip until 15v.
DCv is supposed to be a straight line voltage, semi-impossible to achieve when adapted from AC voltage, good units have seriously very little ripple, as straight as it can be. Cheap units have large ripple, bouncing voltages all over. Makes it hard to get cpus stable, puts undue stress and wear on gpus to maintain performance, fans bounce in speeds, kernal power issues under stress.
Cheap components. They say all Japanese caps, yet fail to mention that all Japanese caps are not equal, there are some that are serious quality, and some that aren't.
Fancy names, titles, rgb fans, modularity, claims. Bling. BS.
Spend $1500 on a really nice pc and power it with a cheaper built psu at your own risk.