Seasonic S12II Bronze 520 W is an excellent power supply. It passed with flying colors in our tests: efficiency between 82.4% and 86.5%, voltages closer to their nominal voltages than required (3% voltage regulation instead of the standard 5%) and ultra-low noise and ripple levels. Plus we could pull up to 588 W from it with efficiency still at 81.7%.
Of course there are power supplies on the same power range from well-known manufacturers that cost less, like Enermax Tomahawk 500 W (USD 70) and OCZ StealthXStream 500 W (USD 40 at Newegg.com, around USD 60 everywhere else), but they provide lower efficiency.
So the real competitor to S12II Bronze 520 W is Zalman ZM500-RS, which costs a little bit more (USD 100), provides lower efficiency at higher loads and has very high ripple and noise levels.
We still think that USD 90 is a little bit too much for this power supply – we’d like it better if it were being sold for USD 80 –, but it is definitely a better product than its competitors. If you are a savvy user looking for a flawless power supply on the 500 W range, this is the unit you should buy.
As a final note, although Seasonic manufacturing quality is flawless, they should take care of the mistakes they are doing on the product label (listing two +12 V rails when in fact the unit has a single-rail design) and product page on their website (chart comparing solid capacitors against regular electrolytic capacitors, which can make users to believe that this unit uses solid caps, which is not the case; listing features that this unit doesn’t have, like OCP).