I saw a Cooler Master Silent pro gold 550W with Active PFC of >0.99, and some others is >0.9.

Base on Wikipedia, Active PFC is also some sort of Electromagnetic filter.

it's talking about the efficiency level.

then is the 0.99 is higher or the 0.9 and 0.99 is the same value ?

No, its is not. PFC stands for power factor correction. Generally in any mains AC system, the voltage and current are both out of phase. This effect causes low efficiency since both voltage and current are not aligned (e.g. when voltage level is present but the current level not equally present). PFC (power factor correction) tries to correct this effect by conjugating both voltage and current to (almost) the same phase. The closer both voltage and current in phase, the better the power factor correction...

When both voltage and current are in phase then PFC will equal "1". That "0.99" is almost as close as you can get to a perfect "1"...

This post has been edited by lex: Oct 16 2014, 01:12 AM

Thanks for the replies, what about the 0.9? some has 0.99. or they is the same?

As mentioned earlier, the closer both voltage and current are in phase the better the power factor. The ideal/perfect power factor would be "1". Thus "0.99" is much closer to that "1", and of course better than "0.9". Its as simple as that...

Below is a simple ilustration of the difference between "without power factor correction" and "with power factor correction"...

Oh, now i understand thanks