Originally Posted by momentten
hmm thanks man .. but in fact i dnt get what r those 12v 5v 3v rail psu ... Is it ok i just find another high wattage psu and use it ?
Ok let me re-adjust and describe it this way. The power supply in any computer converts alternating current (AC) to Direct Current (DC). If you have 120VAC then this is converted to 12V+ and 12V-, 5V+ and 5V- and 3V+ and 3V- within the power supply. These voltages power everything within the computer, including the motherboard, cpu, ram, hard drvies, CD-ROM drvies, fans, lights, everything. All of this is completed using OMH's law. You can read about Georg Ohm here:
Anyway electricity has to conform to his law and we've been using this rule for over 100 years now. The rule is (V) voltage = (I) current times (R) resistance. Given this formula V=I x R we can extrapolate any number of other equations using alegbra. I = V/R or R = V/I Current is also described as Amps and Resistance as Ohms. Anyway what does all of this mean and more to your question. Each power supply puts out so many Watts (W). Watts is the definition of how much work or energy can be completed within given perameters say 500W. However, this involves Ohms law as well. For each 3.3V rail or 5v rail or 12V rail so many amps or current are available based on the power supllies internal construction and setup. What I meant earlier about combined 3v and 5V rails was that some power supplies provide just so much amperage or current and then splits this within the demands of the motherboard board or other demands being placed on it. You want the most stable supply of current to reach all of your devices. So in order to have a stable running PC having a good power supply is an absolute neccessity. Does all of this make sense?? I'm not a teacher or electrical engineer, but I've tried to explain this the best I can without a classroom.
One other link to view: http://techreport.com/reviews/2003q3/psus/index.x?pg=1
If you look down the first page there's a listing of the power supplies max amperages per 3.3/5/12V rails. Remember that some of these amperages are shared between the 3.3V and 5V rails, except the 550W Antec True Power. This power supply provides seperate current supply to each rail and it's adjustable.
I hope this helped, :-)