400W enough?

[Slickone]

I asked over at FW if the PC Power and Cooling Silencer MK III 400W would be enough for most new builds and was told it might not be enough. But after reading a few threads here at AT, when people post a "Is this enough?" thread, seems most of the time ,the regulars suggest that very little wattage is really needed, and that even 300W is plenty in many cases. I don't know exactly what CPU/video I'll get yet, but I never go top of the line because the price jumps up exponentially. And I'm not a hard core gamer, so won't be spending big bucks on top of the line video. So if I build a modern system at least 3.5Ghz (maybe by a mild/moderate overclocking), at least quad core, probably AMD, will a 400W MK III be enough?

 

[dma0991]

If there is only an APU in the build, a 400W PSU is more than sufficient. 400W is sufficient for lower midrange build assuming that the GPU that you're after would only require a single 6 pin or 8 pin PCIE connector or none at all. A molex extension is possible but not advisable. I would prefer to buy a 500W PSU for any builds that I do, it is just more versatile in the types of mid range hardware it will support.

 

[lehtv]

A quality 400W unit can easily power a stock clocked CPU and a modern 28nm video card like 7850 2GB. Such a system will consume less than 200 watts at load (gaming). Even though a 400W unit will only have a single PCIe connector, it'd have enough power for dual connector graphics cards like GTX 670 and HD7950 which only consume around 40W more than a 7850.

 

[Slickone]

A quality 400W unit can easily power a stock clocked CPU and a modern 28nm video card like 7850 2GB. Such a system will consume less than 200 watts at load (gaming). Even though a 400W unit will only have a single PCIe connector, it'd have enough power for dual connector graphics cards like GTX 670 and HD7950 which only consume around 40W more than a 7850.

What about if overclocking CPU? As far as video, I do prefer a standalone video card, but I won't be paying $260 for one (like the 7850 2GB).

 

[lehtv]

If it's a 3570K, overclocking is fine. 3.5Ghz to 4.3-4.4Ghz at stock clocks or so only brings it from 77W to 100W. Nothing to worry about. Even bigger OC's should be fine, it really depends more on your combined +12V load. As long as that stays below 80% of the +12V amp rating, you're fine. In the case of MK III 400W, that's 0.8 * 30A = 0.8 * 360W = 288W. That's roughly i5 @ 4.5Ghz + GTX 680, both running 100%. I know few people would recommend you to run that on a 400W unit... but there's no reason it shouldn't work in the long term.

As far as video, I do prefer a standalone video card, but I won't be paying $260 for one (like the 7850 2GB).

Often cheaper video cards will consume more power because they're older tech. I'd recommend buying the newest generation, e.g. HD 7770.

 

[Slickone]

Wow. Doesn't seem like 400W would be a problem then. Although I'm normally an AMD person (mainly for cost), but not dead set against using Intel.
12V usage would be CPU, chipset, video and RAM?

Also, if it's not maxed out, a 400W should be more efficient than a 500W would be on the same system, wouldn't it?

 

[lehtv]

Also, if it's not maxed out, a 400W should be more efficient than a 500W would be on the same system, wouldn't it?

Not really, only at low loads. See efficiency curve for the 400W unit http://www.techpowerup.com/reviews/PC_Power_Cooling/Silencer_MK3_400W/5.html

 

[Slickone]

Oh I thought thought I'd read here that most PSU's are most efficient at around 80% load. Maybe I read that wrong.

 

[lehtv]

PSU's are most efficient around 50% load, but the difference to efficiency at 20% or 100% load is only a percent or two. Between 400W and 500W units, for example, the difference in efficiency at 200W is not going to be anything you could ever notice in your power bill