Even if he could NOW, power supplies degrade and lose output over time, while the power consumption of the devices connected to it remains the same.  If he decides to upgrade or add on to the system it will in fact rise. In two years, his PSU will be inadequate. ID's nice "nearly new", by then, PC would be seriously underpowered. Figure 80% of original rated output at best by the time the PSU is a few years old.  ID would be best served by a  PSU of 800 watt output, minimum,  IMHO.

 Also, I have to disagree with your belief that the unused capacity of a power supply is wasting electricity. If there is no demand for DC amperage/wattage out, there is no demand for AC amperage/wattage in.  Don't take my word for it, hook an AC Ammeter(mine cost a couple hundred dollars, US) up to your rig and load it up.  If that were the case, PSU's would need a shunt to dissipate all that extra amperage and as Jafo noted, would make a fine heatsource. I've worked on AC to DC convertors and DC to AC inverters for decades and it's been my experience that they mainly get hot in use, not at idle. The higher the demand, the more heat you get. That heat is the wasted energy. Higher rated/more efficient equipment will waste far less, thereby running much cooler.

 and that too........

And I strongly disagree with you. 

Sure, you have a right to an opinion, but your advice re: a 400w PSU is unsound, regardless of the source of information.  To "squeak" by, as you aptly put it, is begging for disaster... especially as the PSU gets older..  So as the others rightly put it, a PSU needs 'overhead' to run efficiently and safely.  Besides, a failing/failed PSU can take out ALL your other components, so for the sake of a few extra bucks it's better to play safe than sorry.

Today I was contacted via Skype by a buddy that helped building a PC for a friend 
What he bought was: 
current gen I5 4670K socket 1150
Asus DCU II GTX 770
Asrock Z87M Extreme4
SSD + HDD  neat Samsungs
2x4GB 1600 DDR3 the brand does not matter and the timings on it simply terrible
AND a 500Watt be quiet "STRAIGHT POWER 10" LOL that name
I would power a Office PC with that has a CPU with integrated GPU


I told him right away that he can power an office PC with tit but not a mid- High Range PC
He did not listen and installed all of the parts, then proceeded and pressed the Power button and nothing but a short beep happened and the Power supply shut down. 
We talked a bit what might went wrong uninstalled the GFX disabled the HDD and only had CPU 1RAM Module and drive hooked PC started.

A GTX770 already consumes up to 300Watts now think about the rest (HDD SDD CPU Keyboard Mouse keep plugging stuff up and poof.)

Also having a High Power PSU does not increase your bill, what does is the Hardware that is hooked up to the PSU, the PSU regulates the output accordingly to the needs of the Hardware?

But I agree if you have an integrated GPU you are safe to run with a 450W PSU like you posted good enough to open mails and play chess.

Running 4 cards in SLI with a 800Watt PSU - Sorry but Quad 980GTX setup will not be able to run a game in Ultra
Settings on more than 720p-1080p without topping 800Watts / despite the fact that you would be mentally disturbed to have 4 of those cards and only run those resolutions and not go for 4K or DSR

Some guys actually running 4xSLi with those already blew up 1500Watt PSU´s like popcorn while overclocking.
That is also the reason why most of them run with a standard of 1000W+ PSU´s

I agree that you can run Quad SLI GTX690 for example on a "good" 1000Watt PSU but that is the absolute limit and those are likely reference cards running at stock speeds.

You could not even run one single GTX770 on that PSU you posted thinking that the rest of the system already consumes 200Watt most likely more.
Not saying that the PSU is shit since it is a Seasonic PSU, only with a corsair label on it.

As posted before there is a reason why we recommend a higher PSU, rest assured that some or many had their experience in buying cheap (sorry) "shit", they rather go for something that lasts especially when it comes to a thing like the PSU.
You NEVER save on something like your PSU.
If you want to save up money or if you do not have enough simply wait or buy a cheaper GFX.

 

As i just see you bought a GTX980 i have a question - once your FPS go over 100 does it the has a "coil whine" it is said that they all have it i can barely hear it with my case closed but it does do have it, so i wonder if yours does the same or if i should simply return it and wait for one that doesnt hae that feature
I know i can simply activate Vsync. 

It's quiet...haven't heard a peep from it...and the Res Evil 5 benchmarker ver has averaged out at 258fps over the couple of minutes it takes to run through.

My case is 3mm 'solid' aluminium [can't really call 1/8" 'sheet metal'] ...so things are going to be quiet, no matter what...

Some do, some don't, and some manufacturers will or won't replace it if yours does. I've only noticed my GTX970 doing it on certain benchmarks and during loading, but then I keep vsync on as I can't stand tearing at all (and don't play multiplayer games with kids where a 1/60 second delay would matter).

I'm used to having it on to keep the old 480 and 580 from going all out and overheating anyway

FYI - just did a quick benchmark and checked the actual power draw; it never broke 320W with the GPU at 99%. That's actual full system draw at the outlet with an i7, factory overclocked GTX970, and monitors included (it's from the real-time display on the UPS). At idle it's under 120W.

I have an 850W supply, since I when I first built this machine I had the GTX480 which was far more demanding (it could draw 300W on its own).

The wattage figures that the GPU manufacturers report as requirements are pretty generous and are for the full system combined. More typically you'd want to check the maximum actual 12v amperage that it supports on a single rail, and I'd bet that was the actual issue in wizard's anecdote above. There are still a lot of supplies out there that split the 12v supply into multiple rails which can't provide enough current for modern video cards (while a single providing the sum current could). Unfortunately the GPU manufacturers don't tend to report the actual current requirements up front any more since the full-system-wattage spec is easier for people to understand.

Overbuying on capacity can impact efficiency as well; even modern 80+ rated supplies don't actually hit their rated efficiency until at least 15-20% load. Below that the efficiency tends to drop off pretty quickly.

That said, one should never skimp on a PSU. Though not necessarily in terms of wattage so much as quality and durability. An easy thing (though not guaranteed reliable) to check is how heavy they are, since that extra weight typically indicates more heatsinks and beefier parts; any PSU that comes with a chassis is generally not going to be a high quality one.

So bottom line--try to target the best quality supply you can find that will cover your system's peak demand, after accounting for inefficiency and loss from aging; an 80+ unit rated at 50% more than your system will ever draw is probably "good enough" for a typical lifespan, and you should land squarely in such a unit's peak efficiency range. Put the extra budget into buying one that is less likely to fail and won't fry your components if it does.

Doing 4 fifths of eff-all my system is drawing 137 watt ...at 88.75% efficiency.

It's called 'idle' but one does not design for 'idle', not when a peak is going to be the wrong side of a PSU's capacity.  That only ends in hurt.

What you look for is reliable, quality components that are up to the task.

As kryo mentioned...'quality' is important...

"3 computer generations ago", ID was probably using the same computer he's finally upgrading today. It strikes me that you and he have completely different expectations about what acceptable performance is.

Is ID going to overclock his machine? Is he going to use SLI? Is he going to hook his microwave up to his computer via USB? If he is, then he will need a bigger PSU. But he didn't mention any of those things. I don't think he will. (Especially for SLI, if he didn't do it now, in a 2-3 years it will be cheaper and easier to just buy a new graphics card.)

I am sure paying over $300 for your PSU was a wise choice, in your case. But it's not clear that it's such a good idea for ID.

Thank you for only reading half my post. The part you missed I believe was this: "get a really high-end 450/500W PSU"

The point is, a cheap 1200W PSU is just as likely to fail as a cheap 500W PSU. But you can get a very nice 500W PSU for a quarter of the price of a good 1200W PSU. We know how much power ID's system is going to draw at peak. Why advise him to buy a PSU that's built to deliver twice as much power?

And yes, a PSU wastes energy. What did you think they're talking about with the Bronze/Silver/Gold/Platinum?

 I didn't miss a thing.  You said that ID could squeak by with a 400 watter... and that is neither wise or acceptable.  As for the 450/500w PSU, a paltry 50w isn't much of a leap, and an extra 100w is neither here nor there should ID want to upgrade his CPU and other components later... I mean, why end up having buy a 2nd PSU when getting the right one first up saves the hassle and expense.

The trend for hardware now is efficiency. In a couple years he'll be upgrading to components that use less power.

I don't understand why you're not advocating for him to buy a bigger processor or telling him to buy several more powerful graphics cards if that's what you think he needs. Instead you're telling him to spend $100+ more on a PSU that he doesn't need just in case...

Just in case he decides to gut the entire machine he's spending ~$1000 on right now.

Edit: I want to be clear that I acknowledge that there are a lot of different perspectives on how to build the perfect system. They mostly revolve around what you plan to do with that system. We don't know what ID's plans are. I am basing my comments on the fact that he has been using the same system for 7 years and based on the specs of the stuff he actually bought.

I think my advice regarding the PSU applies whether you're planning on making a high-powered gaming rig, a bit-coin miner, or an office desktop. You need to get a good estimate of the total peak wattage of your system and buy a PSU that's just past that wattage (15-20%). So if you're planning on putting in a quad-SLI and that needs 1000W, by all means, buy a 1200W PSU. If ID is planning on upgrading to an SLI system then he should incorporate that into his peak wattage calculation.

Actually...the cheap 500 will fail more assuredly when it's limit of capability is more easily reached.

Exact same thing applies with a car.  If it's good/powerful enough to cruise on the highway at 2000rpm at 110kph it WILL last longer than a fart-box at 5000rpm.

Island Dog can use the site I linked to and get SAFER advice than running a 400 watt.

If all it is is a question of 'efficiency' then look for the PSU certification, not how low its headroom might be.

People shouldn't recommend failure to others.  Wobbly advice isn't good for anyone...

You sir, are a car salesman's dream.

True, efficiency is the aim, but ID would need to add just one of these 'efficient' components and he's underpowered, based on what he already has.

Also, have you considered multiple HDDs in your evaluation?   What say he has 6 x2Tb drives; a sound card; a TV tuner and a couple of SATA/USB expansion cards to add from his current machine? 

Nothing like that was mention because ID was referring to the new compnents, but nevertheless, whether he has all these extras or not, the advice still stands.  It is better to be slightly overpowered than to not have enough, as you're advocating.   And nobody is suggesting that ID go for a 1200w or a 1500w PSU.  A 750w to 800w is quite sufficient and certainly not overkill, as it seems you are suggesting.

Put another way, 95% of the streets surrounding you are 35mph/60kmph, therefore I recommend you purchase a car that can do only 36mph/62kmph, no more.  You'd argue that you'd need more power to get yourself out of trouble at times, and I'd argue it isn't necessary, given the prevailing speed limit and road conditions.