Seasonic S12 330W, 120mm Power Supply Review
By: Michael Phrakaysone
Edited By: Steve M. Silver


I’ve never used a generic power supply on any of my computers, and I’m now certain that will never happen in my lifetime. This is because of the numerous times I’ve encountered people coming into the computer store I work at having computer problems. These problems vary from powering up issues, the computer starting to smell, components being fried because lack of power to the system, and random Windows instability issues. These issues were indeed related to the power supply either being blown out or cheap and unreliable.

Seasonic is known for its power supplies being special because of a single reason; efficiency. Seasonic is one of the only companies with power supplies that have the typical efficiency draw of up to 80%. Mostly all other power supplies today come with a typical rating of 60%. So the Seasonic power supplies use only the amount of wattage it needs and will save you cash.

Seasonic’s new power supply series is labeled S12. It is based on the ATX12V v.2.0 specification laid down by Intel and we have it here for review today!

Seasonic’s S12 comes in a very nice and practical box including a handle for you to carry it around after purchase. The box has all the information you will need to know about this PSU.

Specifications and features

General Features

  • Supports the latest P4 Prescott & Athlon 64/64 FX
  • Total Protection: OVP, OPP, OCP & SCP
  • MTBF > 100, 000 hours @ 25c
  • PFC harmonics compliance: EN61000-3-2
  • Supports PCI Express – On 430W+ models
  • Supports Serial ATA interface
  • Universal Free AC input (100-240V Full Range)
  • Independent dual +12V output lines for increased safety & twice the applications.
  • Double the airflow with half the RPM & noise.
  • Outperforms all dual-fan units on the market.
  • Cools your system more quickly and quietly.
  • Longer lifespan due to high CFM, lower RPM and strategic fan placement.
  • Unplug the connectors easily & quickly.
  • Cool, quiet, reliable & energy saving.
  • Saves 15% energy; runs 40% cooler.
  • Includes Dr. Cable organizer
  • Includes external fan control output connectors
  • Dedicated output voltage lines
  • Active Power Factor correction (99% PF)
  • Smart & Silent Fan Control (S2FC)
  • 120mm cyclone cooling fan
  • Ultra ventilation (honey-comb structure grill)
  • Forward converter circuit design
  • Twisted and tidy wires
  • Patented Easy-Swap connectors
  • 3-year warranty


  • Power supply size: 150x140x86mm
  • Maximum power: 330W
  • Efficiency: Up to 80%
  • Industry approvals: UL, CE, DEMCO, NEMCO, SEMCO, FIMCO, CB, FCC, CCC

Specified 330W model voltage rails


There are a couple of notable points here regarding the specifications of the S12. Foremost is the use of APFC (Active Power Factor Correction), which conserves energy and ensures that a clean line of power is given at all times. Furthermore, notice the listed MTBF (Mean Time Between Failures) is rated at 100, 000 hours (you will have this power supply for a long time). Moreover, the S12 has a 120mm fan which helps exhaust heat away from the power supply silently, includes two separate +12v lines which helps prevent a heavy load on a single line and lastly Seasonic provides a 3-year warranty.

A closer look

The Seasonic S12 comes packaged with the following items…

  • Seasonic power supply (the review unit has 330W)
  • Dr. Cable kit
  • Power cable
  • Manual and warranty card
  • ATX 20 to 24-pin connector
  • MOLEX to 3, 3-pin fan connectors
  • Mounting screws

The S12 power supply comes in a black textured metal housing and is quite heavy – that’s always a good sign. The heavier a power supply is, the more likely it has used good components and did not scrimp on material. The exterior has a textured surface that reminds me of stereo equipment.

This version we are reviewing today is rated at 300 watts.

At the top of this power supply you can see the 120mm fan, covered by a silver fan grill to prevent any cutting of the fingers or wires being caught. Throughout testing the S12, the 120mm fan never spun more than 1000RPM and averaged 800RPM. This made for a fan so quiet you could never hear it running. Hard drives are louder than this fan. It pulls plenty of air compared to a 80mm fan as well.

The rear of the S12 maintains the honeycomb design, which allows for maximum amount of heat dissipation and is located to the right is the power cable plug and on/off switch. The S12 automatically senses the voltage range it needs to use to be fully 100-240V compliant.

The S12 is a sturdy power supply. It isn’t as fancy as some other power supplies sporting LED’s but looks like a strong, no-nonsense powerful power supply. Over the months the S12 power supply surface proved to be high quality, prone only to minor fingerprints on the outside. Surprisingly, despite frequent handling in our test rig, the paint never came scratched off the power supply. The quality of paint is shown through its toughness.

The 300watt version of the S12 contains 1 ATX connector (with an included 20 to 24-pin connector), 1 P4 connector, 5 MOLEX connectors, 2 floppy connectors, 2 SATA connectors, 1 PSU fan RPM connector, and 3 external fan connectors (which allows case fans to run at 5V!). The average amount of MOLEX connectors which I look for with a power supply is 6; however 5 is sufficient in this case because the accumulation of other connectors such as 2 SATA connectors which I love.

These MOLEX connectors are not the standard type. Seasonic has chosen to add a thumb grip on them, which makes them a little bit easier to use. I personally like how they work.

All of the wires on this power supply are pre-twisted which helps prevent cable clutter inside the case. Seasonic adds the Dr. Cable kit which helps make them even more clean inside the case. This kit includes 1 split tube, a couple of cable ties, and a plastic cable mount which double-sided tape. Another nice addition from Seasonic.


Testing the Seasonic S12 consisted of idle and load voltage rail readings right after the first install and about 3 months after the inital installation of this power supply. Lastly idle and load voltage readings were taken while maintaining a 200MHz overclock.  Program of choiced used as always was Toast.


Inital install

Idle (30 mins)
Load (Toast 5 mins)
+12V = 11.86
+12V = 11.95
+5V = 4.89
+5V = 4.95
-12V = -11.76
-12V = -11.72
-5V = NONE
-5V = NONE

After 3 months

Idle (30 mins)
Load (Toast 5 mins)
+12V = 11.98
+12V = 12.05
+5V = 5.00
+5V = 5.00
-12V = -11.75
-12V = -11.65
-5V = NONE
-5V = NONE

Overclocked A64 3000+ @ 2200MHz (+200MHz overclock)

Idle (30 mins)

Load (Toast 5 mins)
+12V = 11.96
+12V = 12.00
+5V = 5.00
+5V = 5.00
-12V = -11.89
-12V = -11.75
-5V = NONE
-5V = NONE

The results show the Seasonic S12 already exhibited great voltage rails immediately after it was installed and once approximately 3 months passed, it proved even better. There was very little fluctuation present especially on the 5V rail, and I think this is the best performing power supply I have tested because of the minute movement in loss of power over time. Frankly speaking, I think 330W is enough for about 85% of people’s computers out there.

Other Images


The Seasonic S12 330W power supply is one heck of a power supply. It’s a no-nonsense performing power supply that will meet almost everyone’s needs. It also looks pretty good. I would not fear to recommend this power supply to anyone because this is probably the best power supply I have had the pleasure to test yet. SLi users may want to look into the higher wattage offering from Seasonic to meet their needs.

Pros and Cons

+ Nice looking power supply
+ Solid build construction
+ High quality exterior textured paint
+ Performed admirably
+ Silent!
+ Very little fluctuation even during overclocking
+ 2 SATA connectors and 20 to 24pin connector included
+ 3 Year warranty
+ Worth every penny
-  May not be for the modders who wants LED’s
-  5 MOLEX connectors instead of preferred 6 (minor con)

I would like to thank Seasonic for providing the S12 power supply for review. It was a pleasure to have laid my hands on one. It will be powering my AMD64 system for a long time.

BTW: You can pick one of these bad boys up for around $59U.S at NewEgg and for Canadians.

Editors Choice


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