Common PSU Misconceptions

[hello_there_123]

Some common PSU misconceptions

 

“80+ rating is the best indicator of PSU quality”

 

Not wholly true. You also have to look at ripple, voltage regulation, transient response, noise, fan bearing, topology, load regulation (including 12V crossloads), temperatures (includes rated temperature, 30C 40C 50C etc.). That’s why even though Raider II spinoffs like EVGA GQ and Be Quiet! Pure Power 10/11 are Gold, they are still worse than Corsair CX in quality (ACRF vs Half Bridge LLC). 

 

“You should get a higher wattage PSU because of efficiency curve”

 

First, let’s look at what an efficiency curve on a modern PSU looks like. 

(Left percentage is 115VAC, right is 230VAC) Efficiency peaks at 200/650 = 31% of the rated wattage at ~91.5/93%, then decreases until it hits ~88/92%  at max load and ~87.5/91.5% above 700W. The difference between max load and peak load efficiency is 3.5/1%, which is extremely insignificant. 

Even on older platforms, this trend of efficiency plateauing above ~20-40% load is present:

 

Now for the real world calculations: let’s say that a person is debating on whether to get a 550W or 750W PSU for a build that consumes 400W when overclocked to its max. Also, he’s debating on whether to get the Corsair RMx 550 or 750. 

 

These are the efficiency curves for both: 

The 550W has ~90/92% efficiency at 400W, and the 750 also has ~90/92% efficiency at 400W. Conclusion? He should get the 550 since it’s probably much cheaper, he doesn’t need 750W anyway since his build consumes 400W max, and the efficiency is the same! Source 1 Source 2 Source 3 Source 4

 

“Get more wattage than you need because it will last longer/running your PSU at max will significantly decrease its lifespan” 

 

First off, most modern not trash PSUs are rated for 40C or higher, which is good for most cases. And the advertised wattage is usually CONTINUOUS, not PEAK. If a 550W continuous PSU at 40C were not able to deliver 550W constantly at 40C, then that would be false advertising and the manufacturer would get sued. Thus, the claim that running the PSU at max would significantly decrease its lifespan is generally false. Besides, most PSUs are overbuilt to ~120%+ of their rated wattage, and you can see that from where the protections are set. 

 

More wattage = last longer isn’t necessarily true; a MOSFET or the fan can still fail under high wattage PSUs. In fact, higher wattage PSUs can be more dangerous; this is especially true for single rail PSUs, because highly set OCP (OPP’s even slower!) is much slower than lower set OCP. And in the event of a short within the PSU or within the motherboard, FET/VRM failure on the motherboard etc. the OCP/OPP on the PSU won’t be fast enough to trip before the short causes massive damage on the PSU and/or the motherboard. Source 1 Source 2

 

“PSUs branded by [Brand name] are always good” 

 

Every brand except Delta and Diablotek, etc have made good and bad PSUs (Delta have made only good PSUs if you don’t care about noise, and Diablotek only makes bombs). The most common brands I've seen people spout as “never having made a bad PSU” are Seasonic and EVGA. 

 

First off, both have their fair share of bad PSUs. Look no further than Seasonic’s S12ii/M12ii/EVO series or their S12III series, and EVGA’s G3 (protections are set too high)/BQ/BT etc. 

 

Secondly, EVGA doesn’t even make PSUs (that job goes to FSP, HEC, Super Flower, RSY, Andyson etc.), and Seasonic along with Super Flower often outsource to RSY because their manufacturing capacity is small. If Seasonic/Super Flower choose to manufacture a certain PSU themselves, the Quality Control will be worse on those because every part is outsourced, compared to FSP, CWT etc who do not outsource the PCB-A. 

 

This misconception also falls under statements such as “just get a brand name PSU, they’re all fine”. 

 

“Modularity is extremely important for the consumer” 

 

Truth: unless the person in question is doing Cablemod, Mod vs Semi-Mod will make absolutely no difference, as the cables that are preattached on semimod PSUs will be necessary cables, such as the 24pin for motherboard. Also, in my and many other people’s experiences, on lower wattages (<=550W) nonmod is actually EASIER to work with than semi/full mod because there’s only a few cables left over from nonmod, which are easily ziptied and tucked under the PSU shroud (or left out in the open). Of course the issue of nonmod vs semi-mod is subjective, but at least I have found that the ~2 cables to ziptie after all the cables are attached on nonmod PSUs are easily dealt with. 

 

“Japanese Caps are the most important factor of a PSU's quality” 

 

A PSU is not just a box of caps. There is also the bridge rectifier, transformer, MOSFETs (particularly the 12V ones), fan quality, and topology to worry about when judging a PSU’s quality. The capacitor plague is over; for most modern PSUs, tier 2 Teapo/whatever else caps are as good as Japanese caps, and MOSFETs/the fan are usually the first to fail anyway (Stefan Payne). 

 

“PSU calculators are good for estimating your system’s wattage” 

 

Ever notice how PSU calculators have affiliate links for their recommended PSUs? Yeah, they’re not there for YOUR benefit, they’re there to make money. And in this case, it’s by overestimating the wattage a lot so that they make money off higher wattage PSUs, which cost more thus bringing better profit margins. Outervision is by far the worst offender here; when I put in an RX 5700 XT, 3600, 2x8gb RAM, 1 SSD, 1 HDD, I got ~550W for my power consumption during gaming. However, when I look at Tom’s Hardware power consumption measurements, I see that the 3600 draws about 70W when PBO is turned on during gaming, and RX 5700 XT full OC draws 250W during gaming. Add 30W for everything else (because everything else draws minimal wattage) and we get 350W, which is FAR from the 550W that Outervision proclaimed. 

Be Quiet!’s PSU calculator doesn’t brashly overestimate as much as Outervision’s; when I put in the same specs, I got 387W, which is still overestimating by ~37W but not as much as 550W. However, Be Quiet! Calculator is still overestimating for their own benefit, not yours. Moral of the story? Use THW’s power consumption measurements for the CPU and GPU, then tack on 30W for your true power consumption when gaming and overclocking. Source 1 Source 2 Source 3 Source 4

 

“Get a PSU with higher wattage than you need for headroom” 

 

Nothing about the current trend of CPU and GPU power consumption says that their power consumption will go up in the future. In fact, with die shrinks, the opposite is likely to happen, as same core CPU from Zen+ to Zen 2 power consumption has dropped, similarly with GCN to RDNA. 

 

For example, 450W is enough to run a Vega 56/64 and 8700k overclocked to 4.9ghz (both @Stefan Payne and @LienusLateTips did this). That shows that most builds really don’t need 550W+. 

[Fasauceome]

Did you steal Luke's idea? Also

6 minutes ago, hello_there_123 said:

Look no further than Seasonic’s S12ii/M12ii/EVO series

something something reputation something!!!

[Vejnemojnen]

Is there a way to make this thread sticky? Thank you for writing it. 

[Matsozetex]

I know the Buildapc Reddit is unrelated to this forum. But a post like this would do wonders there.

[hello_there_123]

12 hours ago, Matsozetex said:

I know the Buildapc Reddit is unrelated to this forum. But a post like this would do wonders there.

Most people over at bapo are braindead and resistant to change, lol. This post, especially the Seasonic part wouldn't go over very well for them...

 

Besides PSA's aren't allowed at r/buildapc

[Matsozetex]

8 hours ago, hello_there_123 said:

Most people over at bapo are braindead and resistant to change, lol. This post, especially the Seasonic part wouldn't go over very well for them...

 

Besides PSA's aren't allowed at r/buildapc

You can say that again, especially if anyone talks badly about Seasonic/EVGA. They do allow PSAs, but they do not get pinned, so probably it would be top of the sub for a couple weeks, maybe that is enough?

 

But if you do convince yourself to post on reddit to teach those braind-dead-plebs, I will heavily support you.

 

If you do not want to bother, if you give me your permission, I can do it on your behalf.

[hello_there_123]

16 hours ago, Matsozetex said:

If you do not want to bother, if you give me your permission, I can do it on your behalf.

Well, you could try. But your post will become like 0 upvotes, lol 

[LukeSavenije]

On 9/18/2019 at 1:21 AM, Fasauceome said:

Did you steal Luke's idea?

kinda

 

he asked beforehand, but this aren't my notes

[hello_there_123]

On 9/17/2019 at 7:21 PM, Fasauceome said:

Did you steal Luke's idea?

No, I typed up everything myself

[spartaman64]

i think the headroom part is more about getting a upgrade eg going from a 1050 to a 2080 ti or something

[hello_there_123]

11 minutes ago, spartaman64 said:

i think the headroom part is more about getting a upgrade eg going from a 1050 to a 2080 ti or something

Yea, I could understand paying 5 euro more for a pure power 11 400W over a CX450 for the 6 pin. But what I won't understand is getting unnecessary 650W or above for "futureproofing". 

[Mister Woof]

I used a kilowatt wall meter to test my actual consumption during different loads

 

With everything at full load, and my displays and speakers, the meter read 615w.

 

Subtract maybe 60w from my monitors, another 20 for my speakers and that's like 535w for my system alone at full synthetic CPU/GPU load. Actual gaming or something was closer to 450w (370w after accessories).

 

Still, I could have gone with the 650w PSU but.... It cost the same as Amazon had a sale on the 850.

 

So THERE!

[Spotty]

1 minute ago, Plutosaurus said:

I used a kilowatt meter to test my actual consumption during different loads

 

With everything at full load, and my displays and speakers, the meter read 660w.

 

Subtract maybe 60w from my monitors, another 20 for my speakers and that's like 580w for my system alone at full synthetic CPU/GPU load.

 

Still, I could have gone with the 650w PSU but.... It cost the same as Amazon had a sale on the 850.

 

So THERE!

Plug the PC PSU directly in to the kill-a-watt. Will be much easier than trying to guess how much to subtract for other devices plugged in to it.

[Mister Woof]

1 minute ago, Spotty said:

Plug the PC PSU directly in to the kill-a-watt. Will be much easier than trying to guess how much to subtract for other devices plugged in to it.

 

But then I can't see shit captain. The kilowatt meter is enormous and blocks off the other plugs.

 

Can't start my test if I can't see windows

[Mister Woof]

I suppose I could unplug the other devices after starting but

 

That requires to much effort and the point is moot because price was samesies.

 

Overclocking does tend to throw a lot of the conservative estimates out the window.

 

Overclocked Vega probably accounts for most of the usage in my scenario.

[Vejnemojnen]

On 9/18/2019 at 1:14 AM, hello_there_123 said:

You also have to look at ripple, voltage regulation, transient response, noise, fan bearing, topology, load regulation (including 12V crossloads), temperatures (includes rated temperature, 30C 40C 50C etc.). That’s why even though Raider II spinoffs like EVGA GQ and Be Quiet! Pure Power 10/11 are Gold, they are still worse than Corsair CX in quality (ACRF vs Half Bridge LLC). 

@hello_there_123 could you explain, why the topology of PP11 is inferior? I have personal reasons to ask it, and I thought I might as just ask it here : ) bumping the thread

[PSUGuru]

17 minutes ago, Vejnemojnen said:

@hello_there_123 could you explain, why the topology of PP11 is inferior? I have personal reasons to ask it, and I thought I might as just ask it here : ) bumping the thread

Because ACRF (Active clamp reset forward) is basically double-forward but configured to be a bit more efficient. iirc, it's more difficult to achieve better performance metrics.

Double Forward whines and there's possible transient response issues when paired with high end GPUs. I have no idea if this was verified. I don't know if ACRF exhibits those same things.

[Guest]

1 hour ago, PSUGuru said:

Because ACRF (Active clamp reset forward) is basically double-forward but configured to be a bit more efficient. iirc, it's more difficult to achieve better performance metrics.

Double Forward whines and there's possible transient response issues when paired with high end GPUs. I have no idea if this was verified. I don't know if ACRF exhibits those same things.

They do.  I ordered a bunch of FSP's, tested them and they all do the same thing as any other double forward topology.

[PSUGuru]

14 hours ago, jonnyGURU said:

They do.  I ordered a bunch of FSP's, tested them and they all do the same thing as any other double forward topology.

Good to know. How about the transient issues? Where can I find data on that?