Power supply maximum efficiency and optimal efficiency are two different
things.
Most are rated as 85%+.
However, efficiency curve is best around 40-60% load.
In some cases, that means 850W PSU is overkill, especially, if real load
will be maximum around 300W.
We tested lot of PCs and servers with "powermeter".
Most PCs ended up with total around 100-150W (including monitor).
Typical 2 processor server (DELL 2900, 10 HDD) was 360-390W.
Server which gets 400W+ real load produces a LOT of heat!!!
Trust me. I had such server running at home (temporary) for 2 months.
850W PSU is overkill. 1200W also.
Oversized/overrated PSUs are common, because cheap chinese manufacturers
give incorrect numbers.
Better get good PSU (from known source). It will cost the same money,
and will be more efficient in long term.
Gasha
On 2012-01-08 13:24, AlunFoto wrote:
A bit unfair to say "no hard drives", I think, but I see your point.
Sorry, I just meant that didn't include the cost of any "real" hard
drive capacity, since you're bringing over drive you already have.
Reason I wanted to go with a larger PSU is that I plan to add a second
graphics card (in addition to the RAID disks + an eSATA bay).
850W PSU is enough for two nVidia 560ti cards with the setup you're
discussing and a bit of headroom. 1200 is overkill. You shouldn't need
water cooling for this setup unless you're planning to overclock it.
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