Did you think that rails are only for trains? Well, you are very wrong. Wattage is not the only the measure of the ability of a power supply to support all the components of your computer. The rails are what provide the power to your components.
And even though every voltage requires close attention, you need to pay more attention to the +12V rail or rails which provide power to the components that are most power hungry, as it is from them that the PCIe video cards and processor receive their power.
For a mainstream advanced computer, a modern Desktop Power Supply should output a minimum of 18A on the +12V rail or rails. A modern computer power supply should also output more than 34A (amps) when it powers a high-end SLI/CrossFire system and no less than 24A (amps) for a system that has just a single enthusiast-class graphics card. The precise amperage figure we mean here is actually the combined figure for the PSUs that offer nothing less than one +12V rail. These are some of the power suppliers that are available at 365PowerSupply.com.
3GHW3 03GHW3 CN-03GHW3 495W For Dell PowerEdge R620 R720 T320 Power Supply F495E-S0
What should you look for?
Yes, you should be looking for the combined total output number, but you cannot always calculate the combine output by adding up the +12V rails. For instance, if a Dell Power Supply if is labeled with rails that have been labeled +12V@16A and +12V@18A, you might find out that the unit doesn’t have 34A combine power output, but instead has only 30A. You can always find this information either on the PSU information label or in the detailed unit specifications. Ensure that the +12V rail(s) provide more than 34A combine in case you want to run the SLI/Crossfire configuration.
You should also consider the number of rails that a computer power supply uses to power its components. In simple terms, a Lenovo Power Supply, for example, can provide only one +12V rail to actually provide power to the components of the computer, or it can actually have several rails. A Dell Power Supply with just one rail simply means that all the power is made available to all the PC components that have been connected to it, and that makes configuration extremely easy since there is no need to struggle with matching the components to rails. On the other hand, it also means that a surge, or any power supply failure will definitely affects all the computer components. Multiple rails usually guarantee security against any potential failure. However, they require you to be more careful when setting them up. The same applies to HP Power Supply and any other desktop computer power supply.
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