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Confusing Performance Data On Packaging And Case

Getting the Right Power: 15 PC Power Supply Units

In the PC store, even reading the label tends to confuse the user, because there is usually lots of conflicting performance data. First, we would like to explain the individual performance information using an example:

Confusing performance data on the packaging

The first information, about maximum power (420 watts), is just a reference by the manufacturer to the watt level for the purpose of advertising the power supply unit. It is not important for practical purposes .

Next to this, the manufacturers usually also include the maximum combined power of the +3.3- and +5-volt lines (220 watts) and/or the maximum combined power of +3.3-, +5- and +12-volt lines (400 watts). These numbers indicate the actual power that the +3.3- and +5-volt and the +3.3-, +5- and +12-volt power buses provide in combination. However, since PC components are supplied with power through the "+"-volt lines of the power supply unit, the maximum value for the combined power of the three "+"-volt lines warrants the most attention . That's because this value indicates the maximum power that is really usable for supply the PC components with power.

The "difference" between maximum power (420 watts) and maximum combined power (400 watts) is reserved for standby power and for the -5- and -12-volt lines no longer needed by most systems.

Tip: If the value for the maximum combined power of the +3.3-, +5- and +12-volt power bus is not given, you can calculate a good estimate for this value by subtracting 20 watts from the maximum power.

Not only the power figures, but also the currents of the individual strands are limited: 26 A, 42 A and 18 A are the maximum current of the +3.3-, +5- and +12-volt lines in our example. Good to know: With power supplies in the 300/320-watt class, the maximum permissible currents of the +5V line are about 25%, those of the +12V line average about 15 % less, than a power supply unit in the 400- or 420-watt class.

How a power supply unit should be labeled: Pictured, the HPC420-302 DF from Sirtec

The performance data on devices from Aerocool, Be Quiet, Global Win, Sirtec and Vantec is exemplary.

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