X-bit Labs has compared two passively cooled power supplies; one from Seasonic and one from SilverStone. You can check it out over here.
First goes the 450-watt unit from SilverStone. Although the Nightjar series has been produced for a second year already, Silverstone doesn’t yet offer an alternative. That’s understandable because fanless PSUs are very specific products and their developers focus on achieving high efficiency and use reliable and durable components. Such PSUs have a long lifecycle as the consequence.
The Nightjar series also includes a 300W (SST-ST30NF) and a 400W (SST-ST40NF) model.