Power supply units have a standard size. Essentially, they're large, metal boxes with cable sticking out of them, unless they're modular, in which case they don't have any unless you plug them in. SilverStone's latest invention is different though.
The reason is simple: this is an SFX PSU, for small HTPCs, SFF media PCs, barebones, etc.
Called ST30SF, it measures 125 (W) x 63.5 (H) x 100 (D) mm / 4.92 x 2.5 x 3.93 inches. Not bad for a 300W output, albeit not spectacular either.
Still, the newcomer does have active PFC, a single 12V rail and an efficiency of up to 85% (it's 80 PLUS Bronze certified). SilverStone also implemented an 80 mm fan.
The SilverStone ST30SF should be up for pre-order at €47.89 in Europe and $54.99 in the US. Its MTBF is of 100,000 hours.