Seasonic SS-300FS Active PFC/SS-400FS Active PFC Round-Up Review


Let me thank Sophie Wu from Seasonic for sending their power supplies for review.

The power supply is an important part of a computer. This is what people do not realize. By now everyone should know that. However, purchasing a high performance power supply sometime means the addition of a loud fan thus increasing overall computer noise. Also high performance power supplies tend to be on the $$ side of things. What if you could have a power supply that is powerful and yet is very quiet?

Today we will be evaluating Seasonic’s quiet power supplies. One is 300W and the other is 400W. Seasonic claims that their powers supply units are quiet because of the use of Seasonic’s Patent Pending Technology, the Smart & Silent Fan Control. Will the Seasonic have the power to succeed?

What this does is when the power of the of the power supply rises to it’s maximum wattage output on load (UT 2003, intensive apps) the fan inside the power supply spins faster thus giving better cooling. When the fan is not on load, i.e. Internet, Word. The power supply does not need to spin faster, thus resulting in lower noise levels. The power supply can also control the RPM of the fan during idle and load. To sum it up, when the power consumption is higher the fan spins faster, when the power consumption is low, the fan slows down.

About Seasonic

Profile / Mission / Worldwide service Profile / Mission / Worldwide service
Sea Sonic Electronics is dedicated to offer:
The highest level of quality in design and production, the finest level of customized service and the maximum flexibility to meet our customers’ needs. All backed by a solid company with a strong balance sheet.
The main objective of the company is to develop favorable long-term relationships with our customers.

Incorporated: 1975
Company Type: Public Limited Corporation
Paid-in Capital: USD12,000,000
Head Office: 8F, No. 19, Alley 360, Sec. 1, Neihu Road.
Neihu, Taipei, Taiwan, R.O.C.
Factories: Dong Guan, China, P.R.O.C.(20,000m2)
Tao Yuan, Taiwan, R.O.C. (5,000m2)

First Impressions

300W Model shown, the 400W has a power switch at the rear


Here are the Seasonic Power supplies I will be evaluating. The box presentation is okay with all the information you need. Opening the boxes shows me the units.

As you can see both power supplies utilize 1 fan. This is to maintain the theme “quiet”. He power supplies are quite heavy as that is one of the best ways to tell if a PSU is good or not from my experience. They also look like generic power supplies and we all know what happens with generic power supplies.

What I did not like was the fact that the rear exhaust fan has a metal fan grill that obstructs heat from escaping.


Testing will consist of running both units each at different times. Results of the voltages and case/cpu temperatures comparing it to a 300W Enermax EG-301VP power supply I had previously in my setup.

System Setup

  • AMD ATHLON XP 1900+
  • 2X256 CRUCIAL PC2100 DDRAM
  • 1.44FDD
  • LG 16X DVD-ROM
  • LG 32X10X40 CDRW


400W Voltage Rails first and Enermax 300W rails after to compare.

As you can see, the +5V and +12V rails are lower than what my Enermax offers. The voltages on the +5V and +12V were also spiky. During testing I experienced many problems of instabilities on the computer. It would randomlyt restart and freeze at various times. I checked to see if this was a motherboard problem by putting back the Enermax back in. No reboots, no problems. I put the 400W back in a second time. Same freezing, reboot, and mouse skip problem. I blame this on the +12 and +5V rails.

The 300W model was even worse. It restarted and froze a minute after another. Both power supplies are underpowered and need revising. It rendered my computer useless when my computer would not turn on anymore. As you all know I have not been updating since January 25 and the start of February because of this problem. Luckily I am here today writing this on my old P3 500MHz system that you saw in one of the pictures on the Crystal optical mouse review.

Sound Results – The power supply unit is so quiet that you would not hear it. The first time I started the PSU without connecting it up to the computer turned it off because I thought it was not on. I turn it on again, and put my ear up close to hear it. I felt the air coming out, but I could not hear it when it. It was close to silent levels. Under 25dbA’s from my guess. You have to hear it to believe it. Trust me. This would be great for a quiet PC and a HTPC.


I had problems with the 400W unit. It would restart and freeze at different times. I would not recommend this PSU for a person who has a power hungry rig. It just didn’t have the “umph” to be stable. I blame the voltage spikes for the problems.
However, with that said, I sticked the PSU in a older Pentium 3 500MHz computer with 512MB SDRAM, Mitsumi 4x burner, and a Toshiba 6x DVD-Rom drive and it worked with flying colors. This is the computer I am on today as the test system is down due to problem with the 300W model. The voltages were much stable on the old computer as opposed to my newer computer. Both power supplies worked also. I can only recommend this to people who don’t have power hungry PC’s. If you are a person who has a power hungry PC and you would like quiet…Look elsewhere, this Seasonic is not for you.

I advise Seasonic to try to correct this problems in their power supply line in the future. Go back to the drawing board and make a better power supply that has much better power.

I give the 400W a…


Pros and cons

+ Build Quality Construction
+ Amazingly quiet. Smart and Quiet Fan Control technology works great
- Needs a boost in power
- Single fan
- Not recommended for power hungry PC’s (would restart, freeze) Made test system useless.

I give the 300W model a…

N/A (Did not start on modern power hungry PC. Rendered it useless before I even got to take a snapshot of the rails.

Thanks again to Sophie Wu from Seasonic for giving up her time for us to evaluate these products.


Edit: Feb 12/03

I contacted Seasonic on this matter and they said that their R&D Department are looking in to it and see what they can improve if and when they make a new power supply. This is a good thing, because I know they can improve on this. We look forward in seeing what improvements are in their next power supply offerings.



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