Years ago I tested a 300W passively-cooled power supply from Silverstone and now the firm has finally released a new passive PSU with a bit more power. AnandTech received the SilverStone ST450NF Nightjar, this model delivers up to 450W of power and is cooled by a giant heatsink.
The Silverstone ST45NF Nightjar definitely raises the bar for fanless power supplies, as it delivers one of the best performances from a fanless unit we have seen to date. It even manages to surpass some of the lower quality fan-cooled power supplies. The build quality also sets new standards, as it is excellent. Only a few power supplies have had such high-grade workmanship. The choice of components is generally good, with the important 12V rail using Nippon Chemi-Con and solid state caps and the lower voltage rails getting by with Teapo. The three main capacitors also come from Nippon Chemi-Con and have to fit under the large heatsinks, which is why there are three instead of only one large capacitor. Given the lack of space, Silverstone's internal layout makes sense.
Overall it seems to be a quite good passively cooled PSU but the price is quite high for a 450W model ($170-$190 range). You can check out the full review at AnandTech.