Power supply wattage

I've checked out the sites that let you calculate how big a power supply you
need based on your hardware configurations and all they basically do is add up
the wattage used by each device and add in a small percentage for insurance.
Is that an accurate means of determining power supply needs? I figure that the
biggest power drain comes during startup but does everything (second hard
drives, dvd drives, cd burner, etc.) come on at full power during startup?

On 05 Dec 2004 06:44:03 GMT, ospam (DJS0302)
wrote:

I've checked out the sites that let you calculate how big a power supply you
need based on your hardware configurations and all they basically do is add up
the wattage used by each device and add in a small percentage for insurance.
Is that an accurate means of determining power supply needs? I figure that the
biggest power drain comes during startup but does everything (second hard
drives, dvd drives, cd burner, etc.) come on at full power during startup?

It depends on the particular site. Generally speaking, no,
most of them grossly overestimate the wattage needed. For
example I've bilt multiplie systems that such 'sites claimed
would need over 500W power supply but have already been
running fine for over 3 years with 300W PSU.

Startup is a higher load for a brief moment while capacitors
charge, and longer while hard drives spin up, but once a
system has POSTed at all the typical PC doesn't have enough
hard drives to offset the changes in current caused by a
modern CPU, let alone considering additional demands by some
higher-end video cards.

With older technology is was common for a system to not POST
at all when a power supply had insufficient capacity, and
that's still true today but it's become more and more common
to see systems operating fine until a heavy load is placed
upon them, for example gaming.

This doesn't even consider that some power supplies are less
than accurately rated, having a good system power usage
estimation is only half of the story. If you are trying to
determine the wattage PSU needed for a specific system then
we might be able to better guide if you concisely listed
the components in the system, including makes and models of
parts.