Under the Hood
The Seasonic X Series 400W Fanless PSU is built on the same basic platform as the X-650/X-750. Besides the obvious absence of any cooling fan the X-400 features more heatsinks and larger copper heatsinks. One unique feature shared by all the X Series power supplies is the +3.3V and +5V voltage regulators have been moved off of the main PCB (or daughter cards) and onto the modular DC connector board, which mounts to the front of the enclosure. This is a major innovation that offers several advantages.
• Reduced wiring results in less resistance to current flow and higher efficiency
• Reduced wiring also results in a cleaner layout with better airflow
• Reduced part count results in higher reliability and lower cost
(Courtesy of Seasonic)
The biggest advantage to moving the two VRMs onto the DC connector board is that it virtually eliminates the high current distribution wiring that previously had to route the +3.3V and +5V outputs to the connector panel. This distribution wiring had to carry high currents and therefore was subject to line resistance and voltage losses. With the new design, only +12V has to be delivered to the modular DC connector board, which can be distributed more efficiently with fewer and smaller wires (as voltage goes up, current goes down for the same power).
The X Series main PCB is basically a big +12V PSU that also includes a small -12V regulator and the +5VSB section. All of these output voltages are sent out via modular connectors soldered directly onto the front of the main PCB. A second row of connectors supplies all the peripheral device connectors directly from sockets soldered onto the modular DC connector board.
The main capacitor on the primary is made by Nippon Chemi-Con and is rated at 390uF, 420V, and 105°C. Note that most of the secondary caps are solid polymer type and the copper colored heatsinks are actually solid copper for optimum heat transfer. While certainly unique, this new layout and component selection appears to be excellent.