When I look at the PSUs available these days most of them seem to be 400W and above. Do you really need that much power these days? Onboard GPUs are becoming better and better and other than gamers there isn't that much that the onboard GPU that a Sandy Bridge CPU can't handle. And these Sandy Bridge CPUs don't use a lot of power - certainly much less than a CPU from a few years ago.

SSDs are becoming very cost effective, and a 60GB SSD may be plenty if you have a server in your house to handle media files.

So if you have a PC with a Sandy Bridge CPU without a discrete graphics card, one optical drive, a couple of fans and an SSD then how big do you need your PS to be? Certainly 300W is more than enough, isn't it? And isn't it a bad idea to get a 500W+ PSU if you only are using less than 50% of the rated wattage?

And won't systems like this become more prevalent as Sandy Bridge CPUs become more mature and SSDs continue to get cheaper?

These days? Nothing has changed recently. Peak power has plateaued, but not decreased. Maybe idle power is a little lower. HDs aren't major power hogs in modern systems so SSDs don't change anything.

But using an integrated GPU uses a lot less power and what has changed recently is that there is very little need for anyone, other than a gamer, to need a discrete GPU. Would you ever need more than a 300W PS without a discrete GPU?

The use of a graphics card/unit to accelerate Flash and video playback or encoding software is well established, and has now been joined by GPU accelerated browsers such as FireFox 4 and Internet Explorer 9. So the discrete graphics card has a much wider application than gaming. Even with Sandy Bridge the HD2000 and 3000 on-die graphics units only work with the H61 and H67 chipsets, P67 motherboards still need a graphics card. If anything, the emerging trend is likely to be a use of the on-chip graphics units and a discrete graphics card in combination. An example is Intel's about to be released Sandy Bridge Z68 chipset. And AMD have similar plans for their forthcoming Llano hardware.

In terms of the impact on power supplies, I think you have to look at the noise characteristics of PSUs rather than the nominal capacities. Given, for example, a choice between the Seasonic S380 and the Seasonic X-560 I would pick the X-560 every time because it is quieter and more power efficient that the S380 at low loads. The downside of course is the somewhat higher cost of the X-560, but as ever you only get what you pay for.

No.

Not unless you get funky with Multi-CPU workstations or servers.

Is there really any meaningful difference between say Intel HD 2000 and a discreet card in that sort of application?

Power utilization at idle... for Sandy Bridge quad cores is almost at 0 (4 watts). That leaves the support chips which can't be but a generation behind.

Energy at full utilization looks like it will drop in half with Ivy Bridge utilizing the new Tri-Gate 3D transistors. See:
viewtopic.php?f=28&t=62186

So you would think that the need for power will not go up and in fact appears to be dropping.

Funny thing with the SSDs though... they don't seem to be any more energy efficient... in general... than the mechanical 2.5 drives.

This jump in energy efficiency from the Tri-Gate 3D transistors should permit the Haswell generation ( due out around, or just after, the end of 2012) to pack some heavy duty graphics capability. So while the idle load should continue to drop... it isn't so evident what will happen with the high end load.

We built a system for a customer recently (Sandy Bridge CPU, mini-ITX board, slim ODD + Momentus XT HDD) that had a 150w PSU... which was more than enough. 300w is probably overkill for a lot of what people do!

Mind you... not all that long ago my mother bought a new computer to play Solitaire on and she was sold a 550w PSU because that's apparently "what you need" for modern computers. Some people...

Yes.


It depends. Cost, noise and efficiency at idle/load are all factors.


Yes.

My theory is PSU inflation started when the GPU mfgrs started getting a lot of false returns. The real culprit was a PSU that might or might not have met the ATX spec at the time, but failed to provide enough/stable 12V power to the GPU card. Since they had no control over what PSU the consumer had in their computer, all they could do was inflate the required/recommended power rating, hoping by completely over-specifying the PSU, the darn thing would supply enough 12V current to meet the needs of their power hungry cards.

Move forward 5-10 years.
PSU
- ATX spec is revised with beefier 12V current.
- 80+ (and then Energy Star) requirements drove changes in PSU architecture.
This has led to better PSU designs/implementations. So, the fake need for a 500W PSU turns into smoke. Unless you have a high power 2 GPU setup.

That's the supply side.

On the demand side, all of the hardware uses a LOT less power for a given task. So, a Sandy Bridge setup w/o a separate GPU uses less than 100W.

The problem then becomes:
- PSU mfgrs make more profit on higher wattage PSUs.
- Meeting 80+ at 20% load is a difficult design at lower wattages. That's why the lowest you see from a mfgr you'd want to buy from in the ATX form factor are ~300W and more.
- Consumers are mostly idiots and believe what they read on the interweb/bathroom walls/what their BFF tells them. So, high power PSUs must be good!
- review sites perpetuate the PSU myths.
So, not a lot of incentive for the PSU suppliers to drive lower wattage products out the door.

Net result, we end up looking for the best 300W for our desktops and idle power stifles at 20-30W, when it could be 10W. In the end, this may drive me to getting a laptop to use for an HTPC. Similar specs, half to 1/3 the idle power.

No. PSU inflation started in 1999 with the first AMD Athlon. For that, a 300w PSU was recommended. That was at a time, when NOBODY even knew what kind of PSU they had in their computers. Mind you, we're talking about CPUs, the worst of which drew ~60w of power. For GPUs, we had Riva TNT2s, if we had rich parents. Not sure what their power consumption was, but AGP slots could only provide up to 42w and external connectors were unheard of, so that's that.
Most computers at that time had to be freaks to exceeded 150w, yet everyone was pushing for "at least 300w" --- I remember being told when I ordered that first Athlon. Back then, it was all about "combined power" of 3.3V and 5V. F*ck those PSUs that wasted Amperes on the 12V line. Who uses that?
Oh, good days.

Anyway, that's when the madness started. I remember, suddenly everbody who wanted to be "in the know" was telling you about quality PSUs. Problem was, shortly thereafter, everybody was buzzing about PSUs. So people started to become crazy about RAM. I remember when I bought that Athlon in 1999, memory brands weren't even mentioned in my vendor's brochure. Two years later, everbody "in the know" was telling you to stay away from cheap generic RAM (that's those that grow in the wild) and buy one of them quality brands. Mushkin was all the rage. I remember a friend of mine bought two 256 MB sticks of PC133 SD-RAM with magical Cas Latency of 2 for only 200 bucks a piece. But then again, he never had a lucky hand in these things, he had a pair of the infamous IBM DeathStars in Raid-0. God bless his little heart...

Things haven't changed since then. If you look at forums of the big hardware sites, where 14-year-olds dominate the conversation because they have lots of time and no friends, it's all about RAMs with heatsinks and 500w PSUs for your mom's office PC. But only with one hard disk! If you have two, you better play it safe and get 600w.

Actually the much better question. Would you ever NEED more than a 300w PS WITH a discrete gpu? For most of us silencers, the answer is definitely no. Unless you're running a very high end gpu + cpu, it's extremely likely you will be under 300w. My current system is around 220-230w at max load with a Radeon 6850 + Core 2 duo at 3ghz + a large number of hard drives, discrete sound card, and other peripherals. A solid psu with 300w on 12v would probably work just fine. Of course I prefer something that runs the psu fan at minimum speed, but don't we all?
I would say in general, I bet 90% of the systems we build out here with a single gpu or no gpu would easily fit into a 300w envelope.

Also regarding the no gpu system, the better question would be, would you need more than 175w total? Most cpus are only 65-105w at max, motherboards are maybe 20-25 watts. Hard Drives/SSDs are drops in the bucket. Where exactly are you going to eat power from?

My PSU selection process tends to go:
- What's my expected idle/load power when gaming (my highest power app)?
- Select a well built/reviewed PSU that is:
- inaudible at my expected load
- has decent efficiency at idle and load
- is reasonably priced.

If my load is 230W, I might buy a 300W or a 500W supply. Just sorta depends on how those three criteria stack up with what's currently available. For a few years, I had to buy a PSU rated at 2X my load, simply because their fan profile lead to ramping rpm near/at 50% load.

Now, with the more efficient supplies, there's less waste heat, so the fan profiles are much less aggressive.

I think the "magical" 300W lower limit stem from what tim851 mentioned earlier; those days when the 3.3V and 5V lines were dominating.
As new CPU designs (Pentium 4 and what not) began demanding more from the 12V line it took a higher rated old PSU design to provide sufficient 12V power.
I know from personal experience that a computer can pull quite a bit on the 12V line(s) during startup if multiple HDDs spin up at the same time (pulling about 3A each). That's the real peak in power consumption.

Modern design PSUs can deliver almost all of their rated combined power on the 12V lines, so the power rating doesn't have to be that high.

Cheers
Olle