Originally posted by: CHAROD06
How do I know if my PSU is upgradable? Is is better to have more watts than needed or having the minimun plus little more. I used the calculator, but now I need to know how much extra to get.
Which calculator did you use?
If you used the Takaman calcluator and you're still asking that question, you missed the point.
Wattage isn't everything...
(from my website) All wattage is is the total capability of all of a power supply's rails. The 5V, 12V, 3.3V, -12V, -5V and 5VSB capability all added up. That total number really tells you nothing about the power supply's actual capability. And then, is that wattage continuous power or maximum peak power? There's also variables that come into play like, what was the temperature at which the testing was performed? For what period of time was the testing performed at the specified wattage? Basically, you should look at the amperage each rail is capable of and then just consider that the power supply's BEST CASE SCENARIO capability.
.....You did the calculator, so now you're here.....
Once you do this, you'll really find out how unimportant maximum wattage is, and how important the way the manufacturer distributes power across the rails is. If you have a 500W power supply with 40A available on the 5V line and you're using a Prescott with SLI video cards, you might be in trouble because the 5V line alone is using up 200W of that power supply's total power not leaving much else for other rails! Given that most power supplies give you 20 to 30A on the 3.3V (which is way high by today's standards, but even 30A on the 3.3V is only 100W) and split up about 20W for negative voltage and stand by, you're only left with 180W for the 12V rail. That's only 15A! Mind you, we're talking maximum combined peak power, but better safe than sorry, right?
All that said, fact of the matter is, if you have a power supply that has a load capability properly balance for your PC, you could actually run your machine with a quite a bit of stability with a mere 300W power supply. If you don't believe me, you might want to consider picking up a Kill A Watt. You might find that you're currently pulling about 200W from the outlet. Given that PC power supplies typically only have an efficiency of 75%, that's only 150W!!
...So.... You used the calculator. The calculator tells you how much amperage your
PC could theoretically use on EACH RAIL. Take a look at the label on your power supply. I DON'T CARE IF IT'S A 300W or 900W. Is there any overhead on any of the rails?
Here's a good example using two 500W power supplies (sorry the site is a mess. I'm in the process of migrating the reviews over to SLCentral)....
http://www.webhelp.org/jonnyguru/ultra/ultra-XC500W.htm
http://www.jonnyguru.com/raidmax/index.htm
One power supply (the Raidmax) is clearly made for 5V heavy systems, like an early socket A or a Pentium III system. It did great except for test three which made the 12V drop below +/- 5% spec.
The other power supply (the X-Connect) is made for 12V heavy systems. The 12V was actually OVER SPEC in test two when it was hit with the 5V heavy system, but actually was well within spec during test three when the 12V load was heavy instead.
So bottom line... You can use whatever "500W" power supply you want, but if the power isn't distributed appropriately for your machine across the different rails, you may see similar results (high or low voltages and the instability or overheating that it creates.)
Hope this helps.