I've had my Corsair HX-520 for about 4 days. I couldn't be happier. You really have to put your head within about 12 inches to hear it. If you have a power pig of a system It'll be louder. Listen to the sample sounds on silent pc review.
I like the modular cables. When you have a small case it's nice not to have all of those extra cables stuffed in the case.
Read those review "carefully" if you want to know which model might have performed slightly better than it's cousin. It's like comparing a Plymouth to a Dodge (same engine, different upholstery).
Note that the HX-520 has the same rating on it's 12V lines as the HX-620.
Note that the models smaller than 520W have smaller heat sinks. They will ramp their fans up sooner when the load goes up. It'd be nice if they used the same size heat sinks in the smaller models that they use in the larger models, but then people would have much less reason to select the more costly options.
I am a big fan of PC Power and Cooling, but when it comes to ultra low-noise I think they need to borrow a couple of ideas from Seasonic. Bigger slower fans work better in this arena, period. Making the power supply longer with a space between the fans and the components is not the best approach, and if you're using a small case may be a bad approach.
I'd favor the PC P&C in high wattage apps such as 750W and above. From what I've seen their components are a cut above the rest. In my opinion the single 12V rail is the way to go.
For low-noise I will go with Seasonic (or derivative) until PC P&C gets smart and employs the techniques that are working for the low-noise leaders.
PC P&C doesn't currently make modular power supplies. They can have all the technically (correct) reasons why non-modular is better. If buyers want/need modular then PC P&C should have that as an option.
Don't discount TT completely, some of them are VERY quiet. Mine is a cheapo 470 Watt and it is silent.
Corsair is a bit louder than Seasonic (who makes the Corsair units) but some major caps in Corsairs are better quality, higher temp ratings for some reason (brand differentiation??).
Anyway, for what it is worth, after this PC, I am going to buy EXCLUSIVELY Corsair OR Seasonic.
I got lucky on this PSU, but I only now truly appreciate a good PSU after the problems I had with the stock PSU in a Sonata II that died, and I had such a hard time figuring out what my problems were. Not doing that again EVER.
And which are the new series from Seasonic S12 or M12 and what's the difference ?
The S12 series is non modular and are rated up to 88% efficient. The current S12 series being sold is a newer (this year) generation and part of of 80Plus program for energy efficient PSUs. I have an older generation Seasonic S12 500 and it is extremely quiet.
The M12 series are modular PSU and are rated at slightly lower efficiency of 80% - 85%. They also have two fans one 120mm and one 80mm (or is it 60mm??). Having two fans makes it noisier than the S12, but since it is modular you can better manage the cables.
Between the Seasonic PSUs and Corsair, my preferences are: