Review Index:

Three Seasonic ATX Power Supplies Reviewed

Manufacturer: Seasonic


Editor's Note: The graphs and images are using the original colors and logos as that was the initial release location for this article.

We evaluated the three Seasonic power supplies on both features and performance.  A full range of equipment was used to test each 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.

  • FLUKE 87-III True RMS digital multimeter (Accuracy +/- 0.05% of 3-digit reading) <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

  • WattsUp? Pro — 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 2.1), 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 240 watt combined load to simulate a medium to heavily loaded typical PC.




Here is the Ohm's Law key if you are trying to remember how the different variables relate… :)


 (click to enlarge)

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