I thought good quality PSUs have OVP and UVP, did I misread?
You didn't misread. There's a reason why I said "possibility". Many PSUs that we would define as "good quality" do have OVP and UVP. Not all though, and unless you go looking at a particular model's insides or product propaganda, you'll probably never know for 100% certainty.
Most "good" PSUs should be able to do something ranging from 125% to 150% of designed static load for 10 seconds when
cold.
But (and here's the big "but") you aren't supposed to design a system that relies on that extra margin because it basically means that if you power off the system, you're committed to not powering it back on for several hours so all of the components can be "cold". I believe that the ATX spec says that the PSU has to be able to withstand 110% for 10 seconds when cold.
I've seen systems that are powered off and on weekly and *did* operate above 100% for the first 10 seconds. They lasted several years for that setup (long enough to be decommisioned). That being said, and considering that you shouldn't be powering your system on and off regularly anyway, if you
were to go over 100% a couple of times per year it probably wouldn't ever matter. The only problem with giving a blank statement that it's okay to go over 100% is that you are basically telling someone to take the risk without a full understanding of what they are accepting and we can't generally judge what is a "good" PSU as well as assuming they aren't powering their box off every night like a small percentage of users do despite all of the warnings.
How many people have said they own a "Cyberjock PSU-450" and claimed it was a good brand because it's popular in their country when we all know its total crap?
There is lots of engineered safety margin in these PSUs, but if you are having to rely on them, you've screwed up. As they say at NASA and nuclear power "if you are relying on safety margin to operate, then you have no true safety margin". If memory serves me right, after the Challenger disaster, the appendix that was written b
y Richard Feynman as part of the accident investigation team said something like that when he discussed all of the management issues with NASA and other contracted companies.
So I think the conservative values we've been giving people is still the way we should continue to recommend PSUs.