How expensive would an efficient, good PFC USB wall wart or LED light be?

[Nominal Animal]

This is just a technical question, not about any particular project.

Consider a typical isolated 230VAC to 5.1 VDC 2.1A USB wall wart.  If I wanted it both efficient (at most half a watt of wasted power) and with a really good power factor (say, apparent power no more than half a watt more than real output power), how expensive, complex, and big would it be?

Similarly, if I wanted a constant-current DC voltage for LED lighting from 230VAC (I cannot stand the 100Hz flicker), with good efficiency and good power factor, how expensive would it be (for different ranges of "good")?

The underlying question I am pondering is how difficult and/or expensive will it be to get more efficient and better power factor wall warts and LED lights, when electricity companies eventually start charging even residential users for apparent power.  You'd think a watt here and a watt there does not matter, but in my particular case, those darn things do add up.

[TimNJ]

Currently, wall warts below 75W (or so) don't use power factor. I guess the idea is that a low power device with poor power factor isn't that big of a deal compared to a 1000W power supply with PF = 0.7.

It's not hard, per say, to add power factor correction to a power supply. But it will usually make it bigger and more expensive. For your typical 5-10W USB cube, it's basically impossible to add active PFC and maintain that form factor.

Power supplies used for LED lighting installations are supposed to comply with IEC 61000-3-2 "Class-C". Class-C puts limits on harmonics conducted onto the AC line. For power supplies Class-C compliant and >75W, this means its PFC will be quite good. However, there is still no regulations of minimum PF for power supplies <75W...yet.

[DBecker]

I've seen a number of chips advertised that both use little stand-by power and are power factor corrected.

I don't see them in wall wart or mini-bricks that I've taken apart.  Either they are too expensive, or are very reliable.  I'm guessing the former.  Nobody is paying the distributors to pitch their lowest margin chips.  Only the newest, most expensive solutions.

[TimNJ]

For the most part, low-power bricks don't have PFC because they aren't required to. There is almost no incentive for a general purpose power supply manufacturer to make a low power line with PFC, unless they had a specific customer application. The PFC units would be more costly and wouldn't be able to compete with the competition's non-PFC offerings.

[T3sl4co1l]

Same, I've seen ICs with integrated PFC and regulator for offline DC and LED supply in the 10W range.  Seen in datasheets, that is -- never in the wild.

They're there for when they're needed, but nobody needs to.

As far as expense, most of the expense comes from the lack of quantity.  Instead of $5 for something made in the millions, expect $50 or more for something made in the thousands.  Such is the brutal cut of mass production!

Tim