However saying "Of CoolerMaster V850, barely @120V by virtue of higher efficiency" is nonsense.
Higher or lower efficiency only changes how much extra power is used on the AC side. Take the lowest efficiency and highest efficiency power supply in the world and the DC load is going to be exactly the same.
You also seem to not grasp that LOWER efficiency means for a given observed AC load the DC load is even lower. You correct my use of a (intentionally) high 90% efficiency to point out it was "only 87%" when the lower efficiency would simply mean the DC load was EVEN LOWER. If a unit isn't over spec at 90% efficiency it isn't going to be over spec at 87% efficiency or 1% efficiency.
I understand what you are saying, but when CYPER starts with a wall wattage and says it is "in within specs" you use the efficiency to work backwards from that to find the DC output wattage and therefore if it is within the 840 listed. The entire exercise is a "paper" one, but that's what he presented so that's what I gave him back.
And I "grasp" all of this fine, thanks. You don't seem to grasp what I was trying to convey to CYPER. Read the prior paragraph a few times and let it sink in. You are picking an argument where there is none. I will admit that I did not "show my work" and list in exhaustive detail all the "givens" that went into my statement to your satisfaction since I was just trying to fire off a quick blurb to him, and not you. But if you want it: here is more for you. CYPER listed 900W and said the V850 was in spec. Because of the higher efficiency, it only showed 900W at the wall whereas a HX850 would have shown slightly more owing to its lower efficiency. At 900W, at the listed 90% typical and 93% efficiency at fifty percent load, I used the 90% figure to arrive at a value of 810W DC and thus it was in spec at that wall wattage (though barely..I consider a headroom of 30W to be riding the razor's edge at that level). Obviously, I should have put in a caveat that I would expect the HX to show a higher wall wattage at a similar DC load, and also go into gruesome detail (as I did in the exchange with you later on) about my own observations of *actual* steady sustained and spike power that I observed (although I thought I was alluding to that fact, but perhaps I was too vague). I did not do that, and I apologize that it confused you. Better?
The reality is that those machines pulled more at the wall than what he even cited at times, and thus were out of spec on the spikes rendering that hypothetical exchange moot. Thankfully (for KnC's hosted miners and others) CoolerMaster "V" series units didn't shit themselves and handled the load. The HX850 units (or at least a number of them) did not conduct themselves in the same stalwart nature. At the end of the day, as is my only argument all along, a blanket "850W PSU" recommendation was insufficient and it wound up causing issues. KnC later fixed it with firmware..yay for them..but the initial information missed the mark.