Andre,

My rules of thumb are that most unmodified dealer PC's can easily run at 250
Watts, but once you beginning adding memory, drives, fans, etc., a high end
system should have 300 W for safety's sake.  If you are interested in dual
CPU systems, then you want to consider 400 W.

The science deals with your devices individually and, with effort, you can
determine the maximum power needs for your system.  Check out the following
web site for an explanation and example (go past the price lists for
technical considerations):

http://www.tdl.com/~netex/cases/ps.html

Good luck,
Rand Blunck
Why Not Try Computing
Glendale, AZ

> Is there a specific way to determine when a 250 watt power supply is not
> enough?  All the ide/scsi products inside the computer, plus cpu, fans,
> floppy drive, motherboard, need to be powered. But how can a power supply
be
> monitored to verify it can supply the right quantity of power?  Any rules
of
> thumb or scientific procedures?

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