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Dell offers an extra efficient power supply (PSU) with some products, such as their Optiplex 9010,which I'm considering buying.

They say it's 90% efficient but don't explain exactly what that means or how it compares to the standard. Maybe the standard is 89% efficient, I dont' know.

And the link for "help me decide" is broken.

So I'm wondering what the energy savings % is in standby and full power mode). (From that I can easily calculate my ROI/ Payback period).

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closed as off topic by joeqwerty, Alex, HopelessN00b, Michael Hampton, pauska Nov 1 '12 at 12:29

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Chances are it's a case of greenwashing. – ceejayoz Oct 31 '12 at 18:42

Standby power mode is low. 10% waste (90% efficient) of almost nothing is almost nothing. 30% waste (70% efficient for a poor PSU) is also next to nothing. So ignore standbye.

For full power mode:

  1. Determine how much power is used on average. That will differ per model and per usage. (if you PC is idle while the user merely thinks about which key next to press in office then it will use a lot less power than when it is extracting a multi-megabyte archive).
    Values around 30-80 Watt while idle seem normal.
  2. How much do you pay for electricity?
  3. How much air conditioning do you need (Very roughly: Double the electricity bill).
  4. Is your organisation profiled as 'green'?
  5. Do the efficient PSU's make less noise (less heat wasted means less cooling with the fan in the PSU).

As for what the 'standard efficiency' is:

  • It varies with power drawn. a PSU is usually most efficient at 50% of max load.
  • At less than 10% and more than 90% most PSU get very inefficient.
  • Just about every PSU is > 70% between 20% and 80% load.
  • If it is >80% it will be marked with a bronze rating.

Having said all this, it is useless unless you know how efficient the standard PSU from Dell it. Without that piece of information you can calculate nothing.

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Where I live, we pay over 25c/kwh (3x what it was 10 years ago), so savings will add up fairly quickly if it's noticeably more efficient. If you're paying 10c/kwh then obviously the savings add up very slowly. It makes a substantial difference; after the last price hike we (by chance) upgraded all our servers to brand new Dells from 5-year-old Dells and our power bills went down by over 1/3. – Mark Henderson Oct 31 '12 at 19:21

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