are you suggesting that somehow when these reviewers change only the GPU for testing power consumption that their PSU efficiency somehow is effected by going up or down?
It can, depending on how good the PSU is! It is true that how much a system draws often affects your PSU's efficiency.
PSU's do not have a linear efficiency curve.
"When you open the Power Consumption section in a hardware review, you will usually find power draw data as measured from the wall outlet. However, we use it only when we need to quickly estimate the power consumption of a computer or some other device (a consumer wattmeter is most handy then because it needs no kind of preparation) but not for serious tests. The fact is, although this measurement method is simple, it provides an impractical result....." See full article for explanations.
PC Power Consumption: How Many Watts Do We Need?
How much your system draws at the wall is affected by the efficiency of the PSU. Therefore, what a system uses in the real world in your house depends on how efficient your PSU is @ specific power load level that those components exert on your PSU (and its specific efficiency curve). You also cannot isolate for GPU power consumption without accounting for PSU inefficiency either by just subtracting the total system power consumption.
This is pure math:
Case 1
250W GPU1 + 150W system @ 80% efficient PSU =
500W at the wall
150W GPU2 + 150W system @ 80% efficient PSU = 375W at the wall
What's the difference in power consumption between 2 GPUs? 125W? Not quite! It's "125W, while using an 80% efficient PSU"
Case 2
250W GPU1 + 150W system @ 92% efficient PSU =
434W at the wall
150W GPU2 + 150W system @ 92% efficient PSU = 326W at the wall
What's the difference in power consumption between 2 GPUs? 108W? Note quite! It's "108W, while using a 92% efficient PSU"
If you just looked at Case 1, you'd conclude that GPU1 draws 125W more power than GPU2. That's 100% wrong. GPU1 draws 125W more power only when the system uses a PSU with 80% efficiency. It tells us nothing about what the power difference would be for my system that uses a Silver, Gold or a 92% Platinum rated PSU.
Thus, adjusting for PSU efficiency is critical since all of us have different PSUs. We need the real component power consumption (unless your PSU is exactly the same then this doesn't matter to you), or you have to perform the math yourself on a napkin. If your country uses 240V input voltage and not 120V, your PSU will have a different efficiency as well. You have to account for this if looking at power consumption numbers at the wall in North America.
***Side-note*** Look at the green numbers. By swapping the PSU from an 80Plus to a Platinum,
you just shaved off 66W of power at the wall. Welcome to the world of Platinum PSUs and why they may be worth the cost for enthusiasts who care about power consumption on a heavily overclocked 500-700W gaming system!
The most conclusive and accurate way to compare the real power consumption is at the wall. This is the true power consumption and it is absolute.
"True" power consumption is what the components actually use at the PSU level. Real world power consumption is what those components use at the wall using your particular PSU. Since we have different PSUs and the PSU's power rating also impacts its efficiency curve, if you just measure the power consumption at the wall, it does not apply to another PSU, unless you adjust for the for the efficiency of your PSU. Without this, the review tells me nothing about how much those same components would draw in my own system. If I have a Platinum PSU and you have an 80Plus, you cannot draw any results from the total power consumption numbers of a review that uses a Silver PSU. There is 0 accuracy for your personal needs (unless you make the mathematical adjustments) since your PSU's efficiency is different than that of the PSU used in the review unless you have the same power supply and the same electricity voltage in the country in which you live.
Therefore, you either have to back into the real world power consumption by applying the reviewer's PSU efficiency and then re-applying your own PSU's efficiency rating, or the reviewer has to do this for you from the beginning by isolating the power consumption numbers from the wall, then applying the PSU efficiency and presenting the actual power consumption of the components - say videocard, or GPU, or total system.
The total power consumption at the wall without any adjustment for PSU inefficiency only measures what that
particular system uses at load with that
particular power supply. This has nothing to do with the accuracy or real world use of the said components in another system that has a different PSU with a different efficiency rating. If you understand this when looking at the total power consumption numbers, then there is no problem with showing power at the wall. You can make the adjustments for your own PSU.
If you use a straight up subtraction like you and tviceman are doing, that's 100% wrong because a person using a less power efficient PSU at home than the reviewer's would use more power, while the person using a more power efficient PSU uses less power. In other words, the more efficient your PSU is vs. the one used in the review, the LESS the delta would be between 2 systems in the review in your own home, while the less efficient your PSU is, the MORE the delta would be between the 2 systems for you.
I am with Tviceman on this, and it appears more reviewers would also agree. It seems like a tiny few do not do a total system draw at the wall method.
No, they would not agree. They main reasons they measure at the wall and stop it there is because they are lazy (or don't have sufficient review time) to make the proper adjustments. The ones who do have actually done a better job.
This explains why power consumption at the wall is impractical (
See link above), and pretty much useless unless you make your own adjustments.
You need to understand the context of what it means "At the wall power consumption" if you are going to apply it to everyone on this forum as the universal truth (as you claim the most accurate real power consumption).
No one disagrees that you cannot use the total power consumption of a system at the wall (even though it's not preferable since that means us users have to go through extra steps),
as long as you adjust those #s using the PSU's efficiency used in the review to arrive at the actual real world power consumption of the components. This is because the total system power consumption at the wall changes depending on your PSU's efficiency (i.e., if you have an 80% PSU or a 92% one, etc.)
Now I am going to show you why the 18-36W of power you guys keep talking about is blowing hot air, unless you already have a Platinum PSU!
80% PSU Scenario
System 1 draws
350W of power at the wall (means
280W actual @ PSU level)
System 2 draws 400W of power at the wall (means 320W actual @ PSU level)
Looks like a gamer here has to put up with 50W of extra power consumption at the wall. System 1 looks great!
Now replace that 80% PSU with a 92% PSU:
92% PSU Scenario
Since System 1 only used 280W of at the PSU level, the actual
at the wall power consumption now becomes just 304W (or 46W less than System 1 used at the wall with an 80% PSU)
Since System 2 only used
320W at the PSU level, the actual
at the wall power consumption of this system is now only
347W (or 53W less than used at the wall with an 80% PSU).
And now look at the Blue numbers and the punchline:
A PC gaming system which in aggregate draws 280W of actual power at the power supply level, equipped with an 80% efficient PSU, uses more power in the real world at the wall than another system that draws 320W at the power supply level but uses a 92% efficient PSU.
I just eliminated the
entire 50W of real world at the wall power consumption penalty of the power hungry 400W System #2 against what at first appears to be a more efficient 350W System #1 by swapping an average 80Plus PSU with a more efficient modern Platinum PSU. This means if people are going to throw their arms in the air about such minute differences as 18-36W of total system power consumption on an enthusiast PC gaming rig that pulls 340-350W of power at the wall (or more), every single person who is claiming this 18-36W to be a material difference needs to
immediately go out and buy a Platinum rated PSU. Is everyone here running Platinum PSUs? Didn't think so. So why are we blowing hot air over 18-36W?!
This proves that if you compare total power consumption in a review without accounting for the PSU inefficiency, those #s are meaningless to anyone else that uses a PSU with a different efficiency at home.
So really, unless everyone here has Platinum PSUs, if you are complaining about a 18-36W power delta on your own system that draws around 280-300W of power @ the PSU level, you are just stirring hot air.
If your system has an overclocked Core i5/i7/ Phenom II/X6, etc. + overclocked GPU that uses even more power, if you don't have a Platinum PSU and still discussing 50-60W of power consumption differences as relevant, then please upgrade your PSU to a Platinum one and then I'll take your point more seriously that you really care about power consumption!