At Computex in June, Seasonic showed us an upcoming X Series power supply with an 80 Plus Gold efficiency rating and a partially fanless cooling system. Seasonic now says two X Series units with 650W and 750W output ratings have become "available in the market."
The shipping PSUs still have 80 Plus Gold ratings, which signify efficiencies of up to 90% at a 50% load. Seasonic's Hybrid Silent Fan Control system also switches off the fan if the temperature is low enough. The Engrish-laden press release provides this explanation:
The X Series adopts a clever “Hybrid Silent Fan Control” design, which offers three distinct operation modes, fanless mode, silent mode, and cooling mode. The X automatically adjusts fan mode and speed according to the ambient temperature level. This brand new design not only optimizes heat dissipation, but also prolongs lifespan of the system by reducing unnecessary fan rotation.
Seasonic says it uses San Ace pulse-width-modulation fans from Japanese manufacturer Sanyo Denki.
X Series power supplies also feature solid-state capacitors and modular cabling systems. Seasonic mentions two sets of 8-pin 12V connectors, four sets of 8- or 6-pin PCI Express connectors, and connector sets for Serial ATA hard drives and the usual. You won't find pricing information in the announcement, but we'd expect Seasonic to sell these units at a premium. Just a hunch.