The power supply is another important factor when building a computer. It supplies all the power to your system so this is one component you don't want to skimp on. There are plenty of cheap power supplies out there but usually they aren't very good. The wattage they show (e.g. 430W) is an indication of max wattage rather than true wattage. Max wattage shows the maximum power that particular unit can supply and it very rarely happens. True wattage shows the actual wattage which the PSU will supply most of the time. Obviously, when buying a power supply, you want to know the true wattage of the unit. The Power Supply comes in two main form factors, ATX and BTX, which are meant for their respective Cases which you will see later on.

There isn't any way of telling which method of labeling the power supply uses but usually, if your power supply is made by a reputable brand it should tell you what the true wattage is somewhere on the label of the power supply or if they don't, check the manufacturers website. If you have a generic power supply or a very cheap power supply, then odds are it will show you the max wattage which really is of no use to you. It might have true wattage written down on the label if you're lucky.

Remember to consider how much power your system needs. As a good guide use this PSU calculator. Remember to always buy something a good 50W-100W above the recommendation of this calculator to allow for later expansion for your computer. If you have a power supply without enough power for your computer, it reduces its stability so choose this aspect of your system carefully and always remember to leave a little headroom.

Generic power supplies generally do not last as long as more brand name power supplies do either. This is why it is recommended to buy a good quality power supply for your system. This generally means throwing out the one which came with your case. Reputable brands of power supplies (in no particular order) include Antec, Thermaltake, Coolermaster, Gigabyte, Corsair.

One last thing to look out for when buying a power supply is the connectors it has. Check that it has enough molex connectors (connectors to power your disk drives and hard drives) for your drives or SATA connectors (Also used for disk drives and hard drives but is a newer interface) and if you have a good video card, check that the power supply comes with a PCI express connector. For more information about what the power connectors look like and their purposes Click Here. Below is a simple overview: