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Power Consumption In Standby Mode, Inrush Current, Energy Efficiency

Soon At Tom's Hardware: Full-Scale Power Supply Testing
By , Patrick Afschar

Power Consumption in Standby Mode

As long as the power supply's main switch isn't turned off or the computer isn’t physically disconnected from the power grid, the PSU will consume some power even when shut down. This is called standby power and is required to turn on the PC.

Some computers even provide sufficient standby power to charge a cell phone through a USB port. A constant load on the 5V standby rail (5Vsb) has to be defined and used in order to compare the standby power of different power supplies. We chose 0.25A, which equals a power consumption of 1.25W. The test result shows what the PSU actually consumes in order to provide the required 1.25W. The higher the number, the lower the quality of the power supply in this respect.

Inrush Current

Turning on a computer creates a very strong temporary peak in its input current due to the charging of capacitors and so on. If the inrush current is too high, this could negatively impact other devices connected to the same power strip or even the local power grid if they are really sensitive.

Tom's Hardware tests each PSU to make sure its inrush current stays within the ATX specification of 50A at 230V and 100A at 115V. Our 150A Tektronix TCP150 probe enables us to gather helpful screenshots.

Energy Efficiency According to the 80 PLUS Specification

Next to its power output, the most important characteristic of a PSU is efficiency. It's no surprise, then, that almost every PSU manufacturer out there today advertises the compliance of its products with the 80 PLUS certification. A PSU must reach a certain efficiency under given load percentages in order to use this label.

The different levels (standard, Bronze, Silver, and Gold) symbolize what efficiency level for which the PSU is suitable. The next certification, Platinum, is already in preparation. 80 PLUS has its main focus set on 50% loads, which are most common in everyday use. Tom's Hardware tests whether PSUs are labeled correctly or if certified models comply with the requirements of the 80 PLUS initiative. Since the certification enjoys worldwide recognition, all tests are carried out at voltages of 115V, as well as 230V.

The table shows the criteria the individual 80 PLUS levels are based on.

Energy Efficiency20% Load
50% Load
100% Load
80 PLUS 80%80%80%
80 PLUS Bronze 82%85%82%
80 PLUS Silver 85%88%85%
80 PLUS Gold 87%90%87%
80 PLUS Platinum 90%94%91%


Energy Efficiency Under a Range of Defined Loads

In addition to the efficiency testing done to check the 80 PLUS compliance, we also test the efficiency of power supplies under a number of defined loads. This allows the user to get a picture of PSU efficiency under a range of typical loads. To depict the most realistic scenarios possible, the following loads are used:

  • 25W: Compact all-in-one Atom-based PC without a dedicated graphics card
  • 50W: Office PC without a dedicated graphics card
  • 85W: Multimedia PC with a dedicated graphics card
  • 300W: Gaming PC with a powerful CPU and a modern graphics card
  • 500W: Gaming PC with a high-end CPU and multiple graphics cards
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Top Comments
  • 33 Hide
    Gamer-girl , June 22, 2010 6:24 AM
    Is it possible to include sound levels in decibels?
  • 27 Hide
    JonnyDough , June 22, 2010 6:34 AM
    I second what gamer-girl said, and although this is exciting I'm still awaiting the Graphics Comparison Charts! I realize this is more of an IT website, but these days everyone's a gamer of some type! Long live PC gaming!
  • 17 Hide
    baracubra , June 22, 2010 6:37 AM
    Wow, great idea and article! This will be a huge help and I'm glad u guys took the time and effort to put this together! Long live TH!
Other Comments
  • 33 Hide
    Gamer-girl , June 22, 2010 6:24 AM
    Is it possible to include sound levels in decibels?
  • 27 Hide
    JonnyDough , June 22, 2010 6:34 AM
    I second what gamer-girl said, and although this is exciting I'm still awaiting the Graphics Comparison Charts! I realize this is more of an IT website, but these days everyone's a gamer of some type! Long live PC gaming!
  • 17 Hide
    baracubra , June 22, 2010 6:37 AM
    Wow, great idea and article! This will be a huge help and I'm glad u guys took the time and effort to put this together! Long live TH!
  • 13 Hide
    Anonymous , June 22, 2010 6:42 AM
    take the good ideas from some other nice psu reviewers

    http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=153
  • 3 Hide
    joytech22 , June 22, 2010 6:50 AM
    I hope they do a large comparison, i want to see how my Antec TPQ 1Kw stacks up to some of the other manufactures.
  • 3 Hide
    baracubra , June 22, 2010 6:53 AM
    Btw, how much did all this eqipment cost TH??
  • 3 Hide
    Anonymous , June 22, 2010 7:15 AM
    This is great news. On a related note do you guys not do LCD monitor testing anymore?
  • 4 Hide
    gege , June 22, 2010 7:42 AM
    take the good ideas from some other nice psu reviewers [2]

    www.hardwaresecrets.com/page/power
  • 2 Hide
    liquidsnake718 , June 22, 2010 7:46 AM
    Bravo, good choice for a new section as more consumers and buyers should be aware of the power supplies and the quality/preformance that they offer us. I myself am about to change my older PSU and will be waiting to read the first comparisons. The problem is, which ones will you choose and every month will you have a power category? For example all the 500-600watts, then following the 700-800, 1000w onwards, ect.

    You might even succeed in killing off generic psu's or at least make more ppl buy 80 plus or 80plus bronze psu's....
  • 2 Hide
    Henry Chinaski , June 22, 2010 8:42 AM
    It's a very good news. Another qualified reviewer is always welcome.
  • 4 Hide
    KingArcher , June 22, 2010 9:09 AM
    This is an awesome setup. Wish I worked at TH.
  • -2 Hide
    neiroatopelcc , June 22, 2010 9:31 AM
    Article500W: Gaming PC with a high-end CPU and multiple graphics cards

    I've measured my system using 750W, and that's definetly more than 500W draw on the inside. And considering my system's only got two harddrives and air cooling, I'd say 500W doesn't qualify as high end cpu with multiple graphics! 600W at least!
  • -6 Hide
    Reynod , June 22, 2010 9:52 AM
    Great news.

    We should of course give the reviewer the nickname "Scotty" ... surely?

    The PSU is technically "engineering" and ratings should include references to "warp factor" and dilithium crystals" ...lol.

    Nice test gear there ... good looming job too.

    Looking forward to some definitive reviews now you have the gear.

    I am wondering how some of the vanilla PSU's will go against the more expensive units?

  • 1 Hide
    gustavost , June 22, 2010 10:13 AM
    I can't barely wait for the test!

    It's really nice that we as customers have real test we can rely on!
  • 0 Hide
    feeddagoat , June 22, 2010 11:08 AM
    Bit-tech/CPC already do something like this. Its by far the best way to test PSU's and its fantastic that Tom's is doing something similar. Can I suggest a comment on fan noise as well. bit-tech comment on the loudness of the fan at full load but don't actually do any sound measurments due to background noise in the offices. Better than nothing tho. Also is there anyway to "endurance test" a PSU. A few PSU's end up in secondary PC's, it would be nice if there was someway of testing long term strain on PSU's too.
  • -4 Hide
    7amood , June 22, 2010 11:19 AM
    YESSSSS PLEEEEEEEEEEEEEEASE \^_^/
  • 8 Hide
    allantang , June 22, 2010 11:56 AM
    I wish there were more info on this stuff, so this would be great!

    I think room temp should also be taken into account. It will make a huge difference if the room is 15C or 25C.
  • 0 Hide
    JohnnyLucky , June 22, 2010 12:13 PM
    Great news! Looking forward to reading power supply reviews. Glad to know you will be testing overload and short circuit protection.
  • 4 Hide
    saifallofjmr , June 22, 2010 12:19 PM
    Also please do the green series by rosewill so we can finally confirm whether or not this brand is in fact good or really bad.
  • 0 Hide
    elel , June 22, 2010 12:37 PM
    Good job. Another thing that I think would be VERY useful would be to test the current drawn from each rail by the SBM PCs. I know that you test system wattage already but I would like to see how much current of each voltage they draw, possibly taken from a custom modded high wattage PSU like the one x-bit made for similar measurements.
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