I get the feeling that a lot of people are going way overboard on their
power supply "needs" and I'm at a loss to understand it. I guess it
could be that they are simply buying junk supplies that can't provide
what their ratings might suggest.
Yes, often they are buying generics that have overrated
wattage or are of poor construction. In other cases, they
may be trying to run too close to max output power.
If a system uses 200W continuously, the typical 300W
name-brand PSU is not a good match for long term use in a
reduced form-factor. Downsizing PSU (even "full-sized PS2
PSU in a PC) makes compromises, for example the fan size and
speed, or capacitor size. The heat density becomes
significant. This is not a hard rule, some designs are
certainly better than others but over the years I've even
seem Compaq "90W" PSU that were build disproprotionately
better for long term use than today's Antec 500W or
equivalent in most name-brands. In other words, PS2 (and
smaller) PSU form factor was not designed to scale
indefinitely, it was designed when systems used under 100W.
Systems expected to consume more had larger PSU.
As an example of real world power usage I just checked my AMD box in the
basement. It is an 3500+ Venice with 1gB RAM, five hard drives (four
200gB PATA and one 160gB SATA), one DVD drive, floppy, flash reader, and
an ATI X700PRO with 256mB. Running a program which saturates the CPU (a
weather modeling client) the actual measured power consumption of the
computer never quite reaches 200W. That means that the PS is putting out
a max of 140-150W assuming it is highly efficient. Even if you allow
that I swapped in a real uber-videocard that consumes 100W more than the
current one you are still talking only 250W.
OK, but what size is the PSU? If you had a
reduce-form-factor PSU with 1 cubic inch less space inside,
and the additional space is dedicated to larger part that is
less prone to fail, that is very significant. SFF boxes
have certain limitations.
Take out three or four hard drives since the typical SFF computer only
has space for two drives at most and you are talking a consumption of
maybe 200W max. Even the more puny supplies that Shuttle sells, like the
one presently in my old SB65G2 are rated at 240W and they seem to be
well designed and actually manage to put out what they are rated for.
The newer Shuttle supplies are 300W and seem to be well rated and
reliable as their premium price would suggest.
Which eventually leads to the question: why do so many people seem
convinced that they need a 500+W supply to run their thoroughly average
systems? And we won't even touch the question of why they want to have a
half dozen screaming fans...
Often they start out with a 300W generic, falsely assume the
reason it wasn't sufficient was that "300W" wasn't enough,
and choose a larger wattage PSU thinking that since it
works, insufficient wattage was the problem. It may've
easily been the problem but they had no baseline for what
that "300W" generic was actually able to output.
In other cases, lifespan in particular, it can be a matter
of price-points. A PSU only capable of 200W "could" be
built very well, as OEMs demonstrated for years. One could
swap less than a half dozen components and arguably call
same PSU a 500W model, but running the rest of the
components closer to max ratings will tend to reduce overall
lifespan. IF there were still quality 250W-300W PSU made
at higher price points, instead of budgetized construction,
they would be sufficient for most systems. Unfortunately to
get the quality build one is usually ending up with a 500W
unit even though they didn't need those watts as much as the
rest of the build quality that the higher price-point
allowed.
It doesn't have to be that way, careful PSU selection can
result in savings, but for many the time or experience to do
it isn't worth the difference in cost, they can just choose
a 500W PSU and hopefully have overshot the mark rather than
risk undershooting due to lacking the information to weed
through all the alternatives.
It also becomes harder to find units with very large
amperage on 12V rail unless one also has high amperage
potential on 5V rail, and too few people recognize which
rails their system loads the most. By buying the 500W PSU
they have both bases covered without having to know. It's
not necessary BUT without consideration of the particular
system's needs one cannot qualify a lesser wattage PSU very
easily. Then consider generics where they can't (or at
least shouldn't) trust the labeled capacity and this basic
lack of information makes it more cost and time effective
for an OEM to qualify units for thousands of systems than
the average Joe for only one or two.
I guess I should have labeled this reply as "OT" since it is headed that
way fast. ;-)
Nope, it's relevant... if people want to DIY, they tend to
go overboard the first time (or two or three...) then later
scaling back some with their next systems.