Let me get this straight about PSU’s

[happywormy]

Say I’m getting a 430 W 80+ powersupply. Which one is true:

 

1. It pulls 430 W from the wall and you’re guaranteed 0.8 * 430 W = 344 W

2. It guarantees 430 W but pulls more from the wall: 430 W / 8 * 10 = 537.5 W

 

I wanted to be a 100% sure that’s why I’m asking. Obviously number 1 seems to make the most sense for me, but still.

 

On the sidenote. I calculated how much watt a PC (i5-8600k @ 4.7, GTX 1050 Ti) would use and it’s 364 W. So would an 80+ 500 W PSU from a solid brand work?

[Crunchy Dragon]

The amount that a PSU pulls from the wall varies by how much power the components are using.

[happywormy]

1 minute ago, Crunchy Dragon said:

The amount that a PSU pulls from the wall varies by how much power the components are using.

Lets say it’s using 100% of the power the PSU can handle.

[Crunchy Dragon]

Just now, happywormy said:

Lets say it’s using 100% of the power the PSU can handle.

Then it would take 430W

[QuantumBit]

Pretty sure its the second. Also PSU calculators overshoot. A 450w powersupply will be fine but if you can get a higher wattage for like $5 more, why not.

[TheGlenlivet]

Bought Cheap PSU

[Mira Yurizaki]

2 minutes ago, TheGlenlivet said:

Bought Cheap PSU

Amazing how many people still use the cheap pieces of crap that come with devices that use USB.

[Tabs]

15 minutes ago, happywormy said:

Say I’m getting a 430 W 80+ powersupply. Which one is true:

 

1. It pulls 430 W from the wall and you’re guaranteed 0.8 * 430 W = 344 W

2. It guarantees 430 W but pulls more from the wall: 430 W / 8 * 10 = 537.5 W

 

I wanted to be a 100% sure that’s why I’m asking. Obviously number 1 seems to make the most sense for me, but still.

 

On the sidenote. I calculated how much watt a PC (i5-8600k @ 4.7, GTX 1050 Ti) would use and it’s 364 W. So would an 80+ 500 W PSU from a solid brand work?

 

Your second statement is true. The rating supplied on a power supply is the "maximum combined power" that can be *delivered* by the supply, on the output end, without considering overload situations. The input power will be higher, to account for the losses incurred from converting residential AC to rectified DC rails.

[mariushm]

Good quality power supply from brand names will output UP TO the advertised power (430w, 500w) to components on the 3 voltages : 3.3v , 5v , 12v.

 

Depending on how much power the components take, the power supply efficiency will vary. For example, here's a typical 80% bronze efficiency power supply :

 

 

The picture above shows a Xigmatek 500w bronze efficiency power supply running from 230v AC. At 110v AC, drop around 1% from every point in the graph.

 

So for example, when your computer idles in Windows (browsing some websites, or when watching a movie) the components in your computer will only consume around 80-100w, so the power supply efficiency will be around 82%

When you're gaming and the components demand up to 350w or so, the power supply will be up to 86% efficient.

 

You can translate this to: 

At idle, 100w will be 82% of the total power the power supply takes from the mains socket", so the psu actually uses 100w * 100 / 82 = 122 watts.

At load (gaming), 350w will be 86% of the total power taken from the mains socket, so the psu actually uses 350 x 100 / 86 = 406 watts (56w are wasted as heat inside the psu)

The above power supply can deliver 500w to components (or slightly more, but it's only guaranteed for 500w) with around 85% efficiency, so if you were to have components that use in total 500w, the power supply will take  588w from the mains socket.

 

 

 

 

17 minutes ago, happywormy said:

Say I’m getting a 430 W 80+ powersupply. Which one is true:

 

1. It pulls 430 W from the wall and you’re guaranteed 0.8 * 430 W = 344 W

2. It guarantees 430 W but pulls more from the wall: 430 W / 8 * 10 = 537.5 W

 

I wanted to be a 100% sure that’s why I’m asking. Obviously number 1 seems to make the most sense for me, but still.

 

On the sidenote. I calculated how much watt a PC (i5-8600k @ 4.7, GTX 1050 Ti) would use and it’s 364 W. So would an 80+ 500 W PSU from a solid brand work?

 

[happywormy]

1 hour ago, Crunchy Dragon said:

Then it would take 430W

Take 430 from the wall or what? Everybody else says otherwise.

1 hour ago, QuantumBit said:

Pretty sure its the second. Also PSU calculators overshoot. A 450w powersupply will be fine but if you can get a higher wattage for like $5 more, why not.

Yeah after reading some replies it seems to be 2. So not what I thought. I don’t get why people are so carefull with picking a PSU then. There are all these ratings which seem to have nothing to do with how well your components recieve wattage. It all has to do with how much power it takes from the wall. Why is this such a big of a deal? Would that extra cost of power add up massively after a while?

 

40 minutes ago, mariushm said:

Good quality power supply from brand names will output UP TO the advertised power (430w, 500w) to components on the 3 voltages : 3.3v , 5v , 12v.

 

Depending on how much power the components take, the power supply efficiency will vary. For example, here's a typical 80% bronze efficiency power supply :

 

 

The picture above shows a Xigmatek 500w bronze efficiency power supply running from 230v AC. At 110v AC, drop around 1% from every point in the graph.

 

So for example, when your computer idles in Windows (browsing some websites, or when watching a movie) the components in your computer will only consume around 80-100w, so the power supply efficiency will be around 82%

When you're gaming and the components demand up to 350w or so, the power supply will be up to 86% efficient.

 

You can translate this to: 

At idle, 100w will be 82% of the total power the power supply takes from the mains socket", so the psu actually uses 100w * 100 / 82 = 122 watts.

At load (gaming), 350w will be 86% of the total power taken from the mains socket, so the psu actually uses 350 x 100 / 86 = 406 watts (56w are wasted as heat inside the psu)

The above power supply can deliver 500w to components (or slightly more, but it's only guaranteed for 500w) with around 85% efficiency, so if you were to have components that use in total 500w, the power supply will take  588w from the mains socket.

 

 

 

 

 

Very informative thanks. That cleared things up. So the wattage that manufacturers show is what they guarantee you. So in a PSU’s specs there is no way of knowing if that wattage is actually achievable and THAT’s why solid trustworthy PSU brand are recommended am I right?

 

In short: I won’t per sé need a gold rated supply to oveclock. As long as my wattage and brand are solid.

[happywormy]

Sorry if I got it wrong again I’m trying to get my head around efficiency, wattage, quality, etc

[DragonTamer1]

The PSU should be able to deliver 430W on the output. If that were the case it should draw more than that from the wall. This is not always the case though. That is typically how they are rated.

[mariushm]

Power supplies from no-name brands can sometimes lie about the maximum power they can deliver to components, or express that power in a very creative way (a lie basically).

 

Here's an example of such a power supply that lies on the label, a  hec HP400D RETAIL 400W ATX12V Power Supply :

 

 

You can see they're using 400 in the product code - HP400DB - to trick you into thinking the power supply can output 400w to components, but you can add up the maximum power it can output on 3.3v, 5v, and 12v and see how much it can actually do.  You can see also the note : 3.3v + 5v max combined = 95w

So the above power supply can only provide to components  95w  (3.3v and 5v) + 12v x 11.5A  = 95w + 138w = 233 watts

If you add the 6w it can output on -12v (used by serial ports on motherboards, nothing else) and the 10 watts on 5v stand-by, then this power supply could actually be legitimately called a 250w power supply.

 

Computers these days use 12v a lot, the processor, the video card, the fans and the motors on mechanical hard drives are powered from 12v. You want a power supply that can output the majority of the power on 12v.

The other two voltages (3.3v and 5v) are less important. 5v is still used by the USB ports, by the motherboard (onboard sound, network, chipset) and by the electronics on SSDs and mechanical drives. 3.3v is fairly irrelevant these days.

 

Older power supply designs reserved a portion of the maximum output of a power supply for 3.3v and 5v and another portion for 12v. Here's an example of such a power supply, a Thermaltake 350w one Newegg LINK

 

 

As you can see, this is more or less a 400w power supply which has 90w reserved for 3.3v and 5v and the rest of 312 watts it can provide on 12v where it matters. Even if the motherboard and the SSD or whatever you have on your computer uses only 10-20 watts, the power supply will still reserve 95w aside and will only be able to output up to 312 watts to 12v, even though the power supply is advertised as 350w.

It's not a lie, the power supply can output 350w, even more than 350w, but the condition is that up to 95w must be used by components from 3.3v and 5v and only 312 watts are available on 12v.

 

More modern designs produce all the energy on 12v and then use a DC-DC converter to produce 3.3v and 5v as needed. So for example if all the components in your computer need 20 watts of energy from 5v and 3.3v, then the power supply will take around 22 watts from 12v and produce those 3.3v and 5v outputs with a higher efficiency (up to 96%).

This way, a 450-500w power supply could provide up to 440-490 watts on 12v where it matters, when components don't ask for energy through 3.3v or 5v wires. Here's an example of such a power supply, Seasonic Focus Plus 550w  :

 

 

So as you can see, from 550w of power that can be delivered to components, the power supply can provide up to 540w on 12v where it matters.

If by some exceptional case the components would ask for 100w through 3.3v and 5v wires, then the power supply could still output around 435w on 12v and 100w on 3.3v and 5v.  The dc-dc converter being around 95% efficient, it will need around 105 watts to produce 100w of energy on 3.3v and 5v

The benefit is those 100w are not always reserved to those lower voltages and the power supply can be optimized to be more efficient producing only one higher voltage (12v).

 

 

[mariushm]

Also to add:

 

A power that has an 80plus efficiency report is a minimal assurance that the power supply can output the advertised power to components. Basically, the power supply maker must submit the power supply to a lab, where that lab will test the power supply at 20% of its maximum power, at 50% and at 100% of its maximum power.

 

Now, keep in mind that some less than honest power supply manufacturers can cherry pick some power supplies and send them to be evaluated, or some manufacturers will change some components to make the power supply cheaper... for example they send models with thicker and/or shorter cables to the lab and in the retail model they'll use cheaper thinner cables which cause more losses and therefore lower efficiency. 

 

The labs also often test the power supply at around 20-25 degrees Celsius so in much colder environments. A cheap power supply may pass their tests and output 400-500w because it's cold around it and the fan will push the colder air and keep components happy, but you may have at home 30-40 degrees Celsius inside the case and the cheap power supply may not be able to keep out and output 400-500w at such high ambient temperature.

 

So being rated as 80+ Bronze or better is not necessarily a guarantee that a power supply is good, but it's better than not having a rating at all.

 

 

 

[STRMfrmXMN]

2 hours ago, happywormy said:

Say I’m getting a 430 W 80+ powersupply. Which one is true:

 

1. It pulls 430 W from the wall and you’re guaranteed 0.8 * 430 W = 344 W

2. It guarantees 430 W but pulls more from the wall: 430 W / 8 * 10 = 537.5 W

 

I wanted to be a 100% sure that’s why I’m asking. Obviously number 1 seems to make the most sense for me, but still.

 

On the sidenote. I calculated how much watt a PC (i5-8600k @ 4.7, GTX 1050 Ti) would use and it’s 364 W. So would an 80+ 500 W PSU from a solid brand work?

The wattage you're guaranteed is the amperage on the 12V rail * 12, so usually very close to the advertised wattage of your unit.

 

We have a guide pinned on this subforum about 80 PLUS efficiency. It's also in my signature.

[OrionFOTL]

6 hours ago, happywormy said:

There are all these ratings which seem to have nothing to do with how well your components recieve wattage. It all has to do with how much power it takes from the wall. Why is this such a big of a deal?

Exactly, it's not a big deal. Inexperienced people assume these ratings reflect the quality and performance of the PSU.

5 hours ago, STRMfrmXMN said:

The wattage you're guaranteed is the amperage on the 12V rail * 12, so usually very close to the advertised wattage of your unit.

I think it's misleading to put it like that. The wattage you're guaranteed is the total wattage of the power supply. How it's divided into different rails, and which one is the most important (12V), is just going into the details. A 500W PSU that can provide 200W on 12V and 300W on +5V is still a 500W PSU, just not a very useful one for gamers.

[STRMfrmXMN]

1 minute ago, OrionFOTL said:

 

I think it's misleading to put it like that. The wattage you're guaranteed is the total wattage of the power supply. How it's divided into different rails, and which one is the most important (12V), is just going into the details. A 500W PSU that can provide 200W on 12V and 300W on +5V is still a 500W PSU, just not a very useful one for gamers.

It may be sort of misleading but what's more misleading is calling a PSU a "500W" PSU when it can only output 300W on the 12V rail. I mean, what unit worth its salt has been advertised like that in any sort of recent time?