Articles: Cases/PSU

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This article provides a detailed description of our methodology for testing power supplies. The last article discussing our methodology indepth dates back to January 16, 2005 (X-bit Presents: Power Supply Unit Testing Methodology), and since then additional info on methodology changes has been rather inconveniently scattered among several reviews. So it is high time we posted a new article answering all questions about our testing procedures and techniques.

As our testing methods have evolved and improved over time, some of them may not be reflected in our older PSU reviews just because the method was developed after the publication of the review. The list of changes to this article is provided at its end.

There are three main sections in this article. The first one lists PSU parameters we check out and specifies the test conditions. In the second section you’ll find terms often voiced by PSU manufacturers for marketing purposes and their definitions. The third part will be most interesting for people who’d like to know how our PSU testbed is designed and operates.

When developing our methods we based ourselves on the ATX Power Supply Design Guide standard the latest version of which is available at By today, it has become part of the more comprehensive document called Power Supply Design Guide for Desktop Platform Form Factors in which PSUs of not only ATX but also other form-factors (CFX, TFX, SFX, etc) are described. Although PSDG is not formally obligatory for PSU manufacturers, we think that if not stated otherwise, a PC power supply (selling in retail and meant for general use rather than for specific PC models of a specific manufacturer) must comply with the PSDG requirements.

You can refer to the appropriate section on the site for the reviews of particular PSU models.

Visual Examination

Of course, each test session begins from the tester’s taking a look at the PSU. Besides an aesthetic delight (or disappointment), such visual scrutiny provides some clues as to the quality of the product.

First, it is the quality of the housing as is indicated by the thickness of the metal, rigidity, special features of the assembly (for example, the PSU case may be made from thin steel but fastened with seven or eight screws instead of four as usual), the quality of paint, etc.

Second, it is the quality of the internal component mounting. Every PSU coming to our labs gets opened up and scrutinized and photographed. We don’t focus on minute details and don’t enumerate all the components we find in the PSU along with their ratings. This would make the review more academic, but wouldn’t make much sense for the end-user. However, if the PSU has a non-standard circuit design overall, we try to describe it in general and explain why the developer may have chosen it. Of course, we also draw your attention to any serious defect in the quality of manufacture such as sloppy soldering.

Third, it is the specified parameters of the PSU. The specs are often indicative of quality when it comes to inexpensive PSUs, for example when the total output power marked on the label proves to be much higher than the sum of products of the currents and voltages marked on the same label.

We also provide a list of cables and connectors the PSU offers indicating their length. The latter is written as a sum of numbers, the first of which is the distance from the PSU to the first connector, the second number is the distance between the first and second connectors, etc. The cable pictured above would be described as follows: a detachable cable with three SATA power connectors, 60+15+15cm.

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