I want to build a small PC that will contain an i5-4690 3.5GHz (non k), a GTX 750 TI, 8 GB RAM ( dual channel), a 500 GB HDD and a Mini-ITX motherboard. The components will not be overclocked (and the CPU is non-K anyway).

So will a good 300W power supply work? I know that the GTX 750TI was designed to work with one, and i5's should not take much energy either, but I want another opinion. I checked some websites where they recommend what power supply I need based on my components, and they all say 260W, so I should be good. I also browsed through some forums, but they all seem to be split with half of them (including Tôm's Hardware) saying it's ok, and half saying not good. (the questions people had did not include the GTX 750TI as the videocard though)

So which one is it? Will I be good with a 300W power supply? I know the quality is important, and I found one from Seasonic with a bronze rating and 80+ eficiency. I don't want a higher power supply if not necesary. I could go with a slower clocked i5 if I need to, but it needs to be an i5 not an i3.

I would go no less than 650watt for a build like that.

I'm definitely in the camp of not ok. The 260W seems like a good ballpark estimate, but you will also want some spare capacity. Ideally your components should never exceed 80% of the maximum power supply of the PSU. While it probably will work for a while, you're putting undue stress on a consumer PSU that isn't designed for such things.

I doubt that you will pulling that power all the time, but unless you're only planning to use it as a desktop computer, I'd bump the PSU up to 400W.

Most modern PC's around those specs need less than 300 watts of power, if you got a quality legit 300 watt with high amps on the 12 rail it would be more than fine. Most folks perception of how much wattage is actually used by their own systems is high inflated by misconceptions.

Unfortunately at today's prices you're better off going with a decent 400-500 watt one. My suggestion is this EVGA 500B its's Bronze but only $35 and with rebate card for $15 it's only 20 bucks, it's the cheapest, not garbage, PSU on the market at the moment.

If you want to spend more but get an absolutely amazing one get the Capstone 450 at $46 bucks, yes it is worth it and yes you should buy it over the other because it is a VASTLY superior PSU with much better components.

If you have any aesthetic requirements or preferences let me know. I'll find you something when I get a chance.

The bigger a power supplies maxximum wattage the more power it wastes idle, so a power supply should be as big as necessary and as small as possible. The rule of thumb, your PSU max W shold be 2 times the wattage (TDP) of all your components.

2 * (84 W [for cpu] + 75 W [for video card] + roughly 5 W * [every other component like RAM, HDD, motherboard, drives]) = it all amounts to 350-400 W PSU

I wouldn't recommend seasonic, even when they have even "80 plus gold" ratings, they are cheap(er) because they had problems with buzzing and coil whine. But honestly brand based recommendations are completely worthless, for 3 of the same 380W Seasonic PSUs bought I only had to send back one, but it still was a hassle.

There are no good deals when it comes to PSUs, you get what you are paying for.

@eurobum: so a 350W power supply should be good then, right?

By the way, I googled if a more powerful power supply consumes more when idle and again the opimions are split. Can no one decide?? I usually know when it comes to the stuff I buy, but in this case my knowledge is limited and it sucks. No one seems to say one thing..

I asume one with higher efficiency will consume less?, but generally a lower W power source consumes less? Anyway, a 350W power source with gold rating should be good for me, right?

@zamolxes: with 350W you're cutting it awfully close. Can you even find a decent PSU at 350W gold?

I'm definitely worried about the 12V rail on a 350W psu.

@zamolxes: When it comes to technology there is always someone, who knows better, and as we learn bits and bobs, opinions and priorities might change. Also technology changes and people's knowldege may not be up to date.

Generally low power PSU are more efficient in low power states, but it's always a compromise between price, 80 plus rating and quality. Also low wattage PSUs have a harder time getting a platinum or gold rating because of how the 80 plus certification works. Here's the only comparison showing the general trend.

These intricacies aside it should be a complete no-brainer that a power supply should match power requirements. A power supply is designed to be most efficient around about 50% load, so when Building a PC with a 350 W power supply you can expect that thing to consume around 50 W idle and 175 W when gaming. I have no doubt that you build would work with a 300 W supply, even 200 W.

@eurobum: I'm not entirely sure it will consume as little as 175W. The motherboard does consume a fair amount of power. I'd say he is looking at closer to 200W at load. There is no way of knowing for sure without measuring.

Then there is the question of finding a decent quality 80 plus rated psu at 300W. A cursory search yielded 3 models only, where two of which were manufacturers that I would trust. 80 plus is a rating that doesn't necessarily guarantee quality.

Another thing that OP might consider is that by going with a 300W psu, upgrade or replacement options become much more limited i.e. moving to a more powerful GPU means almost automatically a need to change the psu again.

Smart dudes have given you good advice, but if you're having trouble finding good options at the 300v level (variety is limited) and you want some breathing room for upgradability there are plenty of good 450w sfx12v pus's with high 80 plus ratings.

@zamolxes: The power supply is the one area you absolutely cannot skimp on. I'd rather you cut back on anything else other than the PSU, as you're asking for a world of problems otherwise.

Now, that doesn't mean you need a kilowatt monster in a little build like this, but you should look into something in the 450-500W range. Who knows, you may want to reuse it in some other build down the road, or upgrade what you are putting into this one.

Here's my NASbox build, which used a Mini-ITX mobo, an i3-2200, and no discrete GPU at all. I still went for a 450W PSU. (Granted I have six HDDs in there as well, but my point stands.) Something like this one would sort you out nicely.

There's no way you need 450W. 300W should work great, if you can find a PS you like.

I have a Core i7 920 OC with 24GB of RAM and the beefiest video card I could find that only used one 6-pin power connector. 2HDs, DVD and Blu-ray burners, etc. I ran this config on Antec 380W and 500W power supplies and right now have a 430W in there. The earlier power supplies blew not because of overloading but because my stupid UPS blew them out (as evidenced by that I've years with the latest PS). As measured at the wall, the system never draws over 250W, usually under 100W when doing little and a bit over 200W when gaming.

The number 1 reason people find their PS insufficient is not because it's rated too low but because they are trying to use a PS designed for older systems. New systems draw virtually all their power on the 12V supply, older PSes were designed to put a lot onto the 5V supply instead.

So you'll be fine. Go with 300W modern power supply from a good vendor.

If you can find one used and are looking for as small a build as possible, see if you can find an Alienware X51 on the cheap. They're about the size of an Xbox 360 (possibly a wee bit smaller) and were/are available with i5 and i7 processors. They use an external 330w power supply. I have an R1 (late 2013) X51 with a GTX660, but the system will take a 970 (power consumption on the 970 is actually less than the stock 660).

You could also get one new but given the price the only reason to get one and not build something for cheaper would be the form factor.

Found a size comparison:

Edit: also full disclosure I work for a company owned by the company that makes these. Not shilling, just really like mine.

300 Watts is fine but really you might as well spend just a little bit more and get a nice 430-500 watt one. If you ever wanted to upgrade anything you'd be kinda sol with only 300.

@hobozero: I used to own an X51 before I built my current rig and I enjoyed it quite a bit. You get a lot of performance considering the form factor, I didn't think they could handle a 970 but I guess it makes sense considering the power efficiency.