Power supply readings - am I missing something?


First of all - Happy New Year to everyone!

So just throwing this question/issue I ran into on my newly rebuilt PC - I'm hoping someone has a similar answer or might be able to explain this.

I have an older power supply - an Antec Silent 380W from several years back. The power supply works great, is quiet, and has held up well. Recently I just upgraded several components in my PC (CPU, memory and additional HD's - details below) and thought I should measure my system load (wattage) as I might be nearing a threshold for the CPU.

I purchased a Kill-a-watt meter (4400) and placed that inline with my PC and was shocked at the values. For my PC (specs below) - I easily expected a 300-watt+ load at peak. Instead I found 170W was the max the meter ever showed!

Here's my new PC specs:
CPU - AMD Phenom II x3 720 BE (overclocked to 3.2 Ghz)
Memory - 8 GB RAM
HDs - 2x 7200 RPM Drives
GPU - Radeon 4650
Optical Drive - standard dual-layer DVD
Motherboard - Gigabyte standard desktop board (nothing special)

To perform my "load tests", I performed the following:
1. Windows Experience Index (low usage, I know)
2. Prime95 test for about 30 minutes - got to about 165W
3. Skyrim - full detail - ran around for awhile in game - up to 170W peak.

Maybe there are other tests I should be running too to really push performance, but again, when I did the math on the peak utilization of the components I seriously thought I'd be somewhere in the 300-W range? I even bought a 650W power supply thinking I should prep in the event that I'm 80+% utilized on my PSU.

So is anyone else seeing data like this where their actual usage is significantly less than expected usage? Would you guys still update the PSU just in case? Should I be testing in a different way? Are the kill-a-watt meters off?

Any help, suggestions or comments are greatly appreciated.

7 answers Last reply
More about power supply readings missing something
  1. That's totally normal. Your 4650 is low-end and low-power, and the GPU is usually the biggest power hog in any system. 170 sounds about right.
  2. Kajabla is right.

    The x6xx cards from AMD are scaled back in performance and power from the x8xx and x9xx cards from the same generation.

    The 4000 series was kinda at the peak of power requirements in terms of video cards. The 5000 and 6000 series cards were made with a different manufacturing technique that reduced power requirements even though the cards were more powerful at the same time.

    I don't think that 180w maximum is out of line for a full system with an x6xx card in it.

    I think what is throwing you off is that PSU wattages are usually rated in very aggressive environments (as in like sub-zero room temperatures) that nobody would ever actually run a computer in. In room temperature environments most brands can barely only put out half what it says on the label before running out of spec and many blow up at a little over half of the stated wattage.

    So many 750ws can barely break 300w in continuous power.

    In order to cover their a@@es in terms of lawsuits, so the makers say a wattage high enough where any PSU should be well in the safe zone, even the horrible ones.

    If 95+% of PSU makers didn't straight up lie on the labels, the makers wouldn't have to inflate the requirements so much.
  3. Kajabla / Raiddinn,

    Thanks much for the quick replies.

    So based on the last post that PSU labeling is "very wrong" to start with - if I were even considering a GPU upgrade to the 5000 or 6000 series, should I just upgrade my PSU first to be safe?

    I did just recently purchase a ULTRA LSP650 650W ATX POWER SUPPLY - I was thinking of swapping this in place for my Antec 380W PS.


    Thanks again,
  4. Antec makes great boxes. I think you'd be fine up to around the 6950 range, or maybe the 460. Recent Nvidia cards use a little more power.
    I don't really trust Ultra at low wattages. I'd be more comfortable seeing you stick with the Antec.
  5. The ultra seems to have an Andyson OEM, which is a decent brand. Some of the better brands outsource a couple models to Andyson. Not like Seasonic, but not bad either.

    I looked up a review from an Ultra LSX 750w (closest thing I could find quickly from a serious reviewer) and it said Andyson for that model.

    Anyway, if we assume that the 650w design Ultra is like the 750w design it sent to Andyson, the only thing to worry about should really be the +5 SB power line.

    This line controls waking the computer up from sleep mode and similar things, and you may have problems with that, especially if you plan to have a lot of USB devices continually connected.

    Otherwise, the Ultra should work well enough. It can probably even deliver the wattage on the label.

    That being said, I don't know if it will be strictly necessary.

    Many full systems with 5000 and 6000 series cards still come in under 300w total usage.
  6. Raiddinn,

    I noticed that in your post you show a XFX Core 650W - obviously this is probably a Seasonic PSU like you alluded to.

    I noticed TigerDirect.com has that same model onsale for $64.99 - for that price, is that just worth upgrading to to alleviate any power issues, or from your post, would you just hold off on any PSU upgrades in my case? (Say I were to upgrade even to a 6xxx series Radeon card).

    My Ultra is still within the 30-day return period, so I can return it for a full refund too..

  7. All of the XFX PSUs are made by Seasonic including the model I have, and it is usually regarded as the best brand in the under 1000w range

    If I could return the Ultra and get an XFX of the same wattage I would do it without thinking about it myself.

    When I got mine I wasn't really thinking about the cost, but I did luck into getting it for a very good price ($60 after MIR, so about the same you are looking at), instead I just wanted to have what I felt was the best overall PSU in the range.

    I don't think I made a poor choice with that in mind.

    I think I probably spent 8 hours poring over serious reviews and ripple charts and all of that before I finally settled on the XFX Pro 650w Core.

    Anyway, I like to stick with brands I can trust (in all areas, ex: I buy only Honda cars), but it is just my policy. I don't often shop around to try to save money if it means quality may be brought into question.

    For car insurance, for instance, I won't even consider State Farm insurance. Like a bad neighbor, State Farm likes to go to court to try and avoid paying claims. They usually lose, but they find it worth it to go to court as often as possible anyway. GEICO almost never does this because they have 50 billion in cash ready to pay out in claims and the financial backing of Berkshire Hathaway and by extension Warren Buffett.

    If I get in an accident at some time, I don't want to have to fight with my insurer to get them to pay a claim that they contractually are obliged to pay. I also don't want to fight with my PSU to get it to work when it should work.

    I also drink Coke and not Pepsi, too. I am just really big on brands I can trust. Maybe Pepsi wouldn't let me down, but I would rather not make a serious effort to find out. If I order Coke at a restaurant and they give me Pepsi, I can taste it right away and I send it back for something else.

    Anyway, that is my viewpoint on that sort of matters.

    In any event, the XFX Pro 650w Core will power anything you can stick in there short of multiple very high end video cards.

    One serious reviewer used load testing equipment and managed to pull 815w out of this PSU without damaging the hardware (many PSUs with higher wattage on the label are destroyed with half that much wattage drawn).

    I wouldn't suggest anyone try to sustain that level of load on this PSU over long periods, but its almost impossible to come close to 650w with just 1 video card.
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