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.
Generic or Brand Name?
There are plenty of cheap power supplies out there but usually they aren't very good. Their power can often be inconsistent and not as 'clean' as some better, more expensive power supplies. 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 is almost never reached during every day use. 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 in a tiny font if you're lucky. Generic power supplies often don't last as long either so aren't a good choice if you need a rock solid system.
How much Power?
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 since sometimes your computer may use a little bit more power and if you want to upgrade components in your system (especially the video card) then there is no need to go out and buy a new power supply. I would recommend buying something which might be a little bit more costly since over the long run you won't regret it.
Should I Use the Power Supply Which Came with the Case?
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. Some expensive cases or cases made by the manufacturers of power supplies such as Antec and Coolermaster will give you a decent power supply with your computer which should cover your basic needs and save you a bit of money in the process.
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 as many new video cards need more power than the PCI slot can provide. A good option is to go for a modular power supply. This means that instead of having all of the cables attached to your power supply there are plugs in the power supply so you only need to attach the cables you need. This will mean less clutter in your case as well as better airflow. For more information about what the power connectors look like and their purposes Click Here. Below is a simple overview: