MTP thank you for the charts.
I will use no charts. I will use my rule of thumb.
1. Get more power supply than you need.
The reason is if your system has the capability of a 400W demand a 500W power supply would have to work very hard to keep up. That would create lots of heat and noise from the fan. It would also shorten the life of the power supply.
2. With today's quality power supplies the efficiency at all loads is close to 80 to 90%.
Once again no charts or websites just by my memory and all the research I have done.
Smaller wattage power supplies actually draw more power from the wall socket that a larger higher wattage power supply because you are asking it to work in the 40 to 50% range to keep up and produce heat and noise. A higher wattage power supply would only be working in the 15 to 20% range to do the same job. The fans on my AX-860 and AX-860i seldom come on because they can handle the work load without a sweat and not produce a lot of heat doing so.
3. A higher wattage quality power supply gives you the ability to add things to a computer without upgrading a power supply. Or with a new build you could take the power supply out of old Betsey and use in your new system if need be.
4. Their is no such things as to big of power supply if you are willing to spend the money.
A power supply will only supply the power needed for a system according to the demand.
If your system demands 300W a 500W or a 1000W power supply will give the system 300W and no more. The difference is the 500W power supply has to work harder to do it. Therefor it draws more from the wall socket.
5. The price of electricity varies from location to location.
In my home I have one or two computers running about 12 to 16 hours a day.
The power savings if at all if I went to a so called Green power supply I could make up by turning off a lamp. It cost pennies a day to run my two computer systems. The last time I figured out the price of electricity using my computer systems was less than a Starbuck Coffee per month.
6. Always use a modular power supply. They make a build soooo much easier and neater.
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One of the reasons I don't post a bunch of charts and graphs is because I went through this about year or so ago with another member and all the charts and graphs did was confuse the members trying to select a power supply.
The only reason I don't have a 1000W power supply is because the new build was sneaking up on $3000.00 as it was.
My system will run on a lower wattage power supply quite well but with the AX-860i it will do it cooler and quieter with room to grow.
PS: If one wants the charts and graphs their thousands of website, maybe millions that one can Google.
I think the last site I looked on was Jonny Guru about power supplies but it was a year or so ago.
Please note I keep posting a quality power supply.
If you by a 500W or a 1000W low quality junk power supply you still got a junk low quality power supply.
PC Power Supply Discussion - jonnyGURU Forums
I hope my rule of the thumb helps.