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How We Test Power Supply Units

Voltage Regulation Test

A PSU should be able to keep all of its rails within some predefined voltage ranges at all cases/loads. In Table 1, you will find these ranges (following the ATX v. 2.4 specification).

DC Output Voltage Regulation

Voltage NameRangeMinimumNominalMaximum
+12V1±5%11.40V12.00V12.60V
+12V2±5%11.40V12.00V12.60V
5V±5%4.75V5.00V5.25V
3.3V±5%3.14V3.30V3.47V
-12V±10%-10.80V-12.00V-13.20V
+5VSB±5%4.75V5.00V5.25V

Here's an example of a voltage regulation test results chart you'll find in each of our PSU reviews:

Aris Mpitziopoulos
Aris Mpitziopoulos is a Contributing Editor at Tom's Hardware US, covering PSUs.