PFC in a home use PSU = useless

http://nlcpr.com/Deceptions1.php
Since I'm an electrical engineer specializing in power electronics, I can definitely tell you that PFC adds cost (should be obvious why) and actually *decreases* efficiency! The second part might seem counterintuitive, but consider that PFC is just another stage of power conversion and that in the real world, no power converter is 100% efficient. The slight loss in efficiency is worth it for businesses who are billed by kVA, but home users will not get any benefit from it. (There are also cases where PFC can net an efficiency increase by allowing for a variable rail voltage, but a PC isn't one of them.)

My current machine actually uses a heavily modified server PSU, one of the mods was to bypass the PFC and replace it with a traditional voltage doubler. As expected, the efficiency increased by a few percent when I did that. More significantly, at light load (like only the Atom subsystem running), the total power usage decreased by 15W.

Yet every good PSU manufacturer seems to buy into the scam. Is it that the lack of PFC is associated with low quality, older PSUs? Is it that they want to only manufacture one model of PSU for both home and business users? Is it that most consumers who have no idea think PFC is a good thing? How come I haven't seen a PSU for sale that omits PFC for cost reduction yet is still great quality?

In europe, it's required by law.

Non-PFC units cost you less, but cost the power company considerably more. On the large scale they are significantly more efficient.

In europe some customers are billed based on the apparent power rather than the drawn power, the reason for this is that the power company has to fill the apparent power requirements even if they don't show up on a standard meter.

A non-PFC PSU only uses the tops of the AC waveform, the rest of it goes untouched. The result is that the power company has to generate more power over the entire waveform just to replace that top bit. In essence, a non-PFC uses a ton of power very briefly, 120 times per second.


An APFC PSU uses the entire waveform, it matches its load to the voltage and acts as a resistive load, the power company doesn't have to crank things up to replace the tiny top bit that a non-PFC unit uses, and overall grid power usage and power plant efficiency are much better.

In short, while you the end user (in the USA) might gain slightly, it causes a net loss.


A manufacturer that makes a non-PFC unit cannot sell that unit in europe, hence you don't see many.