Um, yep....why do you think those PSU's were shutting off? And your "spec calculation" is over simplistic, btw...just because a PSU is rated for an overall wattage doesn't mean that an individual rail is.
Simplistic or not it was accurate. Most modern PSU provide 90% to 100% on the 12VDC rail because they do conversion of all AC power to 12VDC and then power the other rails off the 12V rail.
Sorry typo ment to say at worst efficiency was ..... Still if the efficiency was WORSE than 90%, say 88% then that only reduces the relative DC load as it compares to the observed AC load. 850W/0.88 = 956W. 850W/0.85 = 1000W. You telling me people have reported >950W at the wall?
Nonsense.
So once again 850W is fine. A single person reported a single problem with a single model of a single brand of power supply and you want to say 850W is insufficient as a blanket statement. Strange KNC's entire datacenter is powered by nothing but 850W PSUs. KNC still recommend 850W on the site. Many people are using 850W PSUs today without issue. The idea that one needs 1250W or 1600W to power a 600W DC load is well just silly.
Again, according to manufacturer's specs you could expect 87.73% @115V input. So put the lower actual rated rail wattage coupled with lower real-world efficiency and guess what? You are running that thing over-spec at time of KnC initial release and that's why those things were shutting themselves off and then coming back with a bang in some cases upon recovery.
Math isn't your strong suit is it? 840W / 0.8773 = 957W. The LOWER THE EFFICIENCY the higher the observed AC load compared to the actual DC load and power supplies are rated by their OUTPUT not INPUT. So you are actively disproving your point. Now if the unit was 99.9% efficient then yes >850W at the wall would indicate the unit was running beyond peak load. I used 90% because most 80-Plus PSU are within a few % of 90% and certainly don't go much above it on the high end. Still we can use the lower 87.7% that only means the DC load was EVEN LOWER!