The role of a PC power supply unit is to convert the AC electric power that comes from the mains to the DC power that the computer requires. But it can do much more than that. A good quality power supply can make your system more efficient, stable and reliable.
When choosing a PSU the output is very important. This output is listed as watts and should be greater than the combined wattage of all the components in your system plus 40 to 60%. Very simplistically speaking the more demands you place on your system the higher the wattage of the PC power supply unit should be. For example, a high end gamer will require a far higher wattage than a home user who surfs the net and does some word processing.
This universal pc power supply tester tests power supplies from both new and old computers. Since this power supply tester is able to detect the -5V circuit, you will not mistakenly test old power supplies as bad. Most power supply testers on the market do not take this into account, and there is no telling how many good power supplies are being thrown away, no thanks to inadequate testers. This power supply tester also tests the outputs of your power supply so that you can be reassured that your power supply is functioning exactly as it should. Watch the video below the picture to see a demonstration of this tester.