Seasonic X-400 Fanless PSU

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X-400 Fanless (SS-400FL) computer power supply
Sample Supplier
Seasonic USA
Seasonic Electronics
Suggested Price

The primary challenge for a fanless power supply in a computer is the elimination of the heat generated by the conversion from AC to DC. The higher the conversion efficiency, the simpler the task of cooling. The >90% efficiency of the 80 Plus Gold rated Seasonic X-series power supplies is significantly higher than any previous fanless PSUs, so the X-400 Fanless should come as no surprise.

The X-400 Fanless or SS-400FL is the first of two fanless models in the Seasonic X-series power supplies. A 460W model is scheduled to hit the market in September. The X-series is intended to span eight models, with the fanless units at the bottom and 1000W and 1200W models at the top. As SPCR regulars are well aware, a Seasonic X-650 reviewed in November 2009 garnered very high praise and earned our Editor's Choice award. Aside from superb electrical performance, the X-650 featured a successful "hybrid" cooling system — hybrid meaning a cross between passive and active cooling. Its fan simply stopped spinning at loads below ~200W in our hot test box, putting the X-650 at the top of our quiet PSU roster. Interestingly, some of the newly announced 80 Plus Gold Corsair AX series power supplies appear to be direct family relations to the X-series.

Silent PC DIY enthusiasts, especially those building 24/7-on HTPCs, are an obvious target market for the SS-400/460FL, but it isn't that big a market. So what are the other potential markets for fanless PSUs?

  • Specialist system integrators who build high end silent systems, especially home theater PCs where buyers tend to be well heeled and less price-conscious.
  • Specialist laboratory PCs that must not add to either noise or airflow in the test rooms.
  • Digital audio workstations for music production/recording work in studios.
  • PCs in medical applications where high reliability, low noise and no forced airflow are highly valued. (In a premium quality PSU, the fan is usually the least reliable part. PSU makers report that fan-related returns include regular though not numerous instances where the fan blades cut the fan's own power leads.)

Seasonic has been an innovation leader in computer power supply design and manufacturing for over 30 years, and a pioneer in high energy efficiency. Seasonic-made PSUs have also dominated the top ranks of SPCR's Recommended PSU list for years (under its own brand and under the brands of its clients, such as Antec and Corsair). Back in October 2008, Seasonic was the first to achieve the Gold 80 Plus award for ATX12V PSUs, specifically for its 550LT, 650 KM and 750KM models, all using the technology featured in the X-series.

Our X-400 Fanless sample is from the first production batch, the bulk of which should be at retailers warehouses by mid August. Along with the X-400 sample, Seasonic included a reviewer's guide, photos and other technical documentation on a USB flash drive.


The gold-black retail box is similar to others of the X-series. The little box contains the USB flash drive of data and information for reviewers

The packaging and presentation inside is first class, with all the cables in a pouch, and the PSU in a velvet drawstring bag.

Also included are plastic ties and velctro straps for cable management. As with other X-series models, every cable is detachable.

Seasonic X-400 FEATURE HIGHLIGHTS (from the web product page)
FEATURE & BRIEF Our comment
Core Features
80PLUS Gold Certified Super High Efficiency Assured 90% power conversion efficiency.
DC to DC Converter Design; Patented DC Connector Module with Integrated VRM [Voltage Regulator Module]
DC-to-DC conversion for the lower voltage lines is not unusual, but Seasonic's implementation is unique.
Fanless - 0dBA If electronic noise (coil whine) is kept under control, the unit should be silent.
"Green Innovation" Features for Extended Product Life, High Quality, High Efficiency, and Competitive pricing
Highly Reliable 105°C Japanese Capacitors

Many high end PSUs flaunt this feature, including Seasonic's others.

Conductive Polymer Aluminum Solid Capacitors These advanced caps are also used on motherboards.
Super High Efficiency [up to 90%]
Green solution for lowering energy consumption, noise & heat.
Dual Sided PCB Layout
Better utilization of PCB space to enhance quality and performance.
Tight Voltage Regulation [±3%] More stringent than the ±5% recommended by the Intel ATX12V PSU design guide.
Ample +12V Output
33A (396W) on a single rail.
Safety: UL/CUL, TUV, CE, CB, CCC, FCC Class B, C-Tick, GOST-R, UkrTEST, BSMI, Semko Very good.
Protection from short circuits (SCP), over voltages (OVP), over power (OPP), over temperature (OTP), and over current (OCP) The more the merrier. OTP is particular important for a fanless PSU.
Universal Input, Active PFC Like just about every PSU on the retail market... but Seasonic was the pioneer with these features on computer PSUs.
MTBF: Over 150,000 hours at 25 Deg C.
Very good.
Seasonic 5 year warranty Excellent!
Net Weight: 3 lbs 10 oz (w/o cables)
Size: W150 x L160 x H86 mm
Quite light for a fanless PSU.

Seasonic SS-400NF Specifications
AC Input
90~264VAC 6~3A 50/60 Hz
DC Output
Line regulation (all DC rails) ±1%
Load regulation (all DC rails) ±3%
Operating Temp: 0~50°C, 100% Continuous Power @ 50°C

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