A Power Supply Unit (PSU) or SMPS is one of the most important unit of your computer. All other components of your computer depends on it. A good PSU means healthy or good performance of your system. Here are some important things that you should always keep in mind when buying a Computer PSU / SMPS (Switch-mode Power Supply) for your computer.
Brand or Company
This is most basic thing you should look for when getting a new SMPS. Do not go for local brands for SMPS as they can make you pay by causing damage to your important components like motherboard, processor and graphics card in your PC. These local branded SMPS are mostly china made and do not supply proper current and voltages to your components. Their stickers might say 500 watts but in reality they do not have capacity of even 250 Watts. So the main point is that go for Established Brands which are known to produce high quality products like Antec, Cooler Master, Corsair, Tagan, VIP etc.
12 Volt Rail Current
Every SMPS unit has a table printed on them that shows the voltages and current for different rails in the SMPS. Here look for the 12 Volt column and see the current under it. Make sure it has at least 32 Amperes of current listed under it. For dual 12Volt rails, each rail should have at least 18 Amperes of current under them. 12 Volt rail is the most important unit in the Power Supply of your computer, it is responsible for supplying current to the major components of your PC that includes Processor, Motherboard, Graphics Card and others. A higher Wattage SMPS can sometimes have small current under 12 Volt rail, so first look for the 12 Volt rail current and then look for SMPS wattages.
Cooling also forms the most important part in the SMPS. A better cooling will ensure proper functioning of the device under heavy load. A good SMPS must have big 120mm fan and more heat-sinks to provide proper cooling to the Power Supply Unit. You can check the weight of the SMPS by feeling it in your hand, heavier the SMPS better is the cooling as it will have more heat-sinks installed in it.