The computer power supply unit is a hardware designed to convert power from the mains to specific voltage that's required to run a computer. It also regulates the supply of power to the machine, which is very important, considering that minor fluctuations in the same can lead to some serious damage to the machine. Simply put, it is not just required to run the machine, but is also necessary to make sure that the machine is safe from volatile power supply from the mains. Taking the importance of this unit into consideration, it isn't surprising that experts stress on the fact that one has to be careful when choosing it. Tips to Buy a Computer Power Supply Unit (PSU) Many people assume that buying power supply for the computer is an easy task, which can be done with a snap of the finger. Some go to the extent of assuming that the unit with highest output is the best option for their desktop. With that in their mind, they buy the unit with maximum power, but ignore the vital aspects that need to be taken into consideration. Wattage: It is undoubtedly the most important aspect of the PSU. Normally, the units meant for desktop computers range between 400 to 1000 watts, but units reaching up to 2000 watts are also available. Units with such high wattage are most often used for servers and computers with multiple processors. Various software and online power supply calculation applications can help you determine how much power you will require. Ideally, you should buy a PSU that exceeds your power requirements by 30 percent. It will save you the task of having to purchase new unit when you upgrade your PC. Connectors: The PSU connectors determine the capability of your machine. There is a vast range of PSU connectors available in the market. Some models have 24 pin connector, while some have a 20 pin connector. You need to make sure that the connector is compatible with your system. Most of the Pentium 4 CPU-based motherboards, for instance, require a 20 pin connector, while the subsequent models require a 24 pin connector. Efficiency: Even though your PC has 400-watt power supply, the amount of energy that the unit draws from the wall or the mains is estimated to be a lot higher than that. The efficiency of the unit is determined by the amount of energy lost when the unit converts the power from the mains to suit the requirements of the computer. So it is ideal to choose a PSU which is highly efficient (HE) in terms of energy consumption. A PSU with 85 percent efficiency would mean that 15 percent of energy is lost in the form of heat. Higher the efficiency, lesser will be the energy loss. Application: You also need to analyze the purpose for which you would use the computer. In this case, you need to take into consideration the present as well as the future use of the machine. If you are using multiple processors, or if you plan to use the PC for gaming or networking, it's better to opt for a power supply unit with extra wattage. Even if you are not an expert in computer hardware, being well-versed with these basics will help you make the right choice. Ignoring them, on the other hand, will result in you opting for the wrong unit, which will either come heavy on your machine ... or your pocket.