The power supply is a box inside the computer that converts 115 Volts AC (Alternating Current) to the 5 and 12 volts DC that the electronic components use. In Canada and the USA the mains are 115 volts. In Europe they are 230 volts +10% or -6%. In Scotland they are 240 volts. In India you may have 90 to 230 volts coming from different outlets in the same room. Most power supplies have switch to adjust for input voltage. If it set incorrectly you could do major damage. Higher voltage makes for more efficient transmission, but increases risk of death from electric shock.
The best quality power supplies are PC Power and Cooling Turbo-Cools. The extra expense may be worthwhile if:
If have problems with severe sags or power outages, you also need a UPS (Uninterruptible Power Supply).
After years of shrinking power requirements, the new multi-core, 3+ GHz CPUs (Central Processing Units) need more and more power. The CPU (Central Processing Unit) chip itself can use 140 watts. The modern CPU needs a number of auxiliary fans and heat sinks to keep it cool. Most cases and motherboards are now ATX (Advanced Technology Extended) form factor. There is not enough room in a µATX case for the power supply, the giant CPU, the elaborate GPUs (Graphics Processing Units) and all the cooling fins and fans. Premium power supplies are now 500-900 watts where in the 1990s they were 300 watts.
Better brands include: Antec (be careful, there are different companies with similar names), Cooler Master, Corsair and Silverstone. Some of the features you might look for are special CPU cooling features, high efficiency, premium quality bearing fans, quiet fans, and fans that slow down when the machine is running cool so they can lower noise.
When you buy a power supply, make sure it is exactly the right size to fit in your case and that it provides the matching connector types and voltages that your motherboard requires. Measure the size of your current power supply and look for an exact match or one you are absolutely sure will fit. Happily power supplies seem to have standardized on 150 × 140 × 86 mm. A cheapie power supply may mean your machine will lock up frequently for no apparent reason. If the fans are inadequate it will half the lives of your other components and hard drives. The good news is most modern power supplies shut themselves off if they overheat.
When selecting a new power supply, check the size to make sure it will fit. Also check the connectors to make sure you have everything you need for your peripherals, motherboard, CPU fan, aux fans… Sometimes power comes via the motherboard, sometimes directly from the power supply. The best power supplies are active, mid-range are passive and cheapest are non-PVC. You need to oversize your power supply so that you keep it running below 60% capacity. Nothing too awful will happen if you get a power supply too big. It won’t use that much extra electricity.
For my upgrade, I selected the Cooler Master Extreme Power Plus RS-500-PCAR-D3 I chose this power supply partly because it comes with 15, count-’em connectors. This gives be the flexibility to add pretty well any new or legacy peripherals. It has a honking huge fan and intelligent fan controller. It is Energy Star compliant. It in an active type. It claims 70% efficiency, slightly on the low side.
In the old days, there was an AC cord from the power supply to a large switch on the front panel. Now there is a 5 V connection from the front panel power switch to the motherboard. You short the pins momentarily with the front panel switch to power on or power off. The motherboard relays that request to the power supply. In addition, the power supply might have an AC override switch mounted on the power supply. Make sure nothing can bump this switch unintentionally. Your computer will not power up until the connections from the front panel are attached to the motherboard.
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