The S12-600 has the largest output capacity in Seasonic’s new S12 series of PC power supplies and is both environmentally friendly (active PFC), highly efficient, and runs cool and quiet.

Seasonic continues to expand their ATX form factor power supply lineup and today we have one of the new S12 series (Silent 12cm fan series) units up for review.  The S12-600 is rated for up to 600 continuous watts output and complies with the latest ATX12V v2.0 specification.


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Seasonic has been designing and manufacturing power conversion products since 1975.  Their customers have traditionally been in the telecommunications, networking and IT industries.  Today, Seasonic offers a full line of switching mode power supplies that are well suited to the PC enthusiast market and backed by a 3-year warranty. 


Seasonic S12-600 Features

·         High capacity 600 watt output (continuous)

·         Dual +12V outputs (up to 18 A each)

·         Multiple 12V connectors (4-pin ATX, 6-pin PCI Express, 8-pin EPS)

·         120mm Cyclone cooling fan

·         Smart and Silent fan control

·         Active Power Factor Correction

·         High efficiency operation


The Seasonic S12 power supply was evaluated on both features and performance.  A full range of equipment was used to test the power supply under controlled load conditions.  In addition to measuring the power going in and coming out we looked at voltage regulation, electrical noise (AC ripple), airflow, sound level, efficiency and cost.  Here is a block diagram of the test bench setup and a list of the equipment I used during testing.


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  • FLUKE 87-III True RMS digital multimeter (Accuracy +/- 0.05% of 3-digit reading)
  • Power Angel — digital wattmeter and power analyzer (Accuracy 3% of displayed value)
  • Hitachi V-650F 60 MHz dual trace oscilloscope (Accuracy +/- 3% of input range)
  • Powerstat Variable Autotransformer, 1.4 KVA, 0-140 VAC
  • FLUKE  52-II digital thermometer (Accuracy +/- 0.3ºC/0.5ºF)
  • Extech Model 407736 digital sound level meter (Accuracy +/- 1.5 dB)
  • AccuLab V1-10kg digital balance (Accuracy +/- 1g)
  • Homemade power supply load tester — selectable load, up to 300 watts


To be ATX compliant, a power supply must be designed and built according to a set of standards created by Intel (ATX Specification — Version 2.2), which along with motherboard specifications also defines the size, form factor, connectors, voltage outputs, etc., that a power supply must incorporate.  More detailed information can be found in the ATX12V Power Supply Design Guide. 


The switching-mode power supplies used in modern PCs are designed to convert alternating current (AC) into direct current (DC) used by the computer’s internal components.  A standard ATX power supply will produce three different voltages to power the motherboard, CPU, memory, hard drives, optical drives, etc.  These are: +3.3 volts, +5 volts, and +12 volts.  In addition, the PSU also generates several other voltages: -12 volts and +5 volts STBY (note: the -5 volt output was removed in ATX12V rev. 1.3).


Establishing a controlled load is critical to testing and evaluating a PC power supply.  I built my own power supply load tester using 11 wire-wound, ceramic resistors of various sizes.  This unit can place up to a ~300 watt load onto the power supply being tested.  Different combinations of resistors can be switched in or out to select various loads.  I will be using a 263 watt combined load to simulate a medium to heavily loaded typical PC   In addition to my own load tester, I will also be using the load tester kindly provided by Seasonic





The Seasonic S12-600 power supply is rated for a combined continuous load of 600 watts (many if not most PC power supplies are marketed using the peak load value, which is considerably higher).  The S12-600 has been designed and built to comply with the latest Intel ATX12V v2.0 specifications.  In addition to the power supply the package also includes a power cord, mounting screws, printed User’s Manual, 24-pin to 20-pin ATX adapter, special 5V fan adapter cable, and a package of plastic spiral wrap and wire ties for cable management.


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The S12-600 incorporates active power factor correction (PFC) and the unit can automatically select the proper input voltage so there is no manual AC voltage selector switch on the rear panel — just the power cord receptacle and On-Off switch.


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The 24-pin main power connector provides additional power leads for +3.3V, +5V and +12V rails as required by some newer motherboards.  In addition, there are two separate +12V outputs (main 24-pin power connector and three 12V connectors) that can both supply up to 18 Amps each.

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