the average user doesn't need a second power supply, power users
and overclockers alike (that's us) tend to use gadgets that
require a lot of power, much more than the ordinary power supply
can handle. Fans, TEC units, water pumps (some of them), and
more recently lights or neon are all things witch you can plug
on your power supply. If you system require more power then
your power supply can give, your system will be highly unstable.
But why not simply get a new, more powerful power supply? Well
first of all you have to understand something. You have some
parts of the system like the memory witch require 3.3v while
others like hard drives require 12v and 5v. What really interests
us here is the 12v line. Since most, if not all overclocking
gadgets work on 12v, this is the voltage that you will need
A typical 250w power supply is able to put out 10amps at 12v.
This means that out of 250w total, only about 120w is available
through 12v (amps x volts = watts). This is exactly the reason
why you can't plug a 120w peltier on a 250w power supply. When
buying a bigger power supply, make sure it gives you enough
power at 12v. The 300w power supply I have only gives 10amps
at 12v, just like my 250w. The additional 50w is available for
the 5v and 3.3v lines so it does not help me at all. Other 300w
power supplies will give 12amps at 12v. The biggest power supply
I have seen was rated at 450w and could supply 16amps at 12v,
this gives you 192w of power at 12v but will cost you over 100$.
What you could do instead is buy two cheap 250w power supplies
and link them; this would give you about 240w of power at 12v
for under $50. As you can see, multiple smaller power supplies
will give you more power for less money.
you probably know, an ATX power supply will not work if it is
not plugged to a motherboard. Since you cannot plug two power
supplies into a single motherboard, the first logical step would
be to find a way to make a power supply confer power without
being plugged to a motherboard.