This may help figure your power supply needs and give you a way to go about finding out yourself.
Each component that is installed in your computer will draw some wattage and depending on what the component is will determine how much.
Most components will state what their power draw is and the two biggest draws are the CPU and the video card. When upgrading or building your computer these two will be the top draws.
One of the most helpful things to get a feel for what's needed is a Power Supply Calculator.
This software tool will help you configure the total draw of the components that you have so you can know what you computer is useing or going to use.
When going to buy the Power Supply now that you have a rough idea of what you need you will have to decide the type , standard , semi-modular or fully modular.
Standard being all the cables are attached , semi-modular is where some of the cable are left off and you can attach those as needed and finally fully modular is where all the cables are not attached and you only attach those that are needed.
How many watts did the power supply calculator come up with and you take that number and add some extra to give yourself a bit of a cushion. Next you want to see how many hard drives and dvd drives you will have so that you get enough Sata power connectors with the PSU that your looking at.
You also want to know how many video cards you will have so that you have enough 6+2 pin and 6 pin cables. A three way video card setup will require 2 separate cables for each card and a total of 6 all together.
One of the most important pieces of information about the PUS is how many +12v rails does it have and the amperage on each rail.
Looking on the side of the PSU or in the specifications of the unit you will be able to see that information. Some manufacturers will make their PSU with several rails, as many as 8 on occasion while others will make one massive rail. On multiple rail units the total amps will be divided between the rails. This can be ok but when installing video cards that have a high demand for amps you want to make sure that it's getting the amps needed.
A single rail will have no issue providing all the amps needed and some of the more advanced power supplies come with the option to chose single rail or multiple rails.
Building a normal computer with a single video card and average CPU will not require much in the way of specialized options. If your the type to do your own troubleshooting then a power supply tester is a handy tool to have.
To add a second power supply for the real power users you can use a connection like this for adding a second or supplemental power supply.
Last but not least is the brand name of the power supply as you don't want the cheapest there is and most can't afford the most expensive so a bit of research into reliable brands will help in obtaining a good dependable PSU that will last .