I do not run any over clocking, and I have measured the pc's to currently use less than 30Watts, this should leave plenty power to run some of the peripherals from the pc power supply. It is a 200Watts standard power supply, and even though it may not be able to deliver all of that much power, I think I can at least get some 75% of the listed max. Amps.

Using a D-sub9 female connector (to make it different from the serial port) I now run my External IOmega CD-burner using this power source.
I have also added mini-jack connectors for 12V  external power.

One of the added bonuses I get from using the pc power supply for external boxes is that I can now unplug all those little transformers that seems to be colleting in greater and greater numbers. My last count reached 16 such transformers.

And each of them draw current, even when the device is turned off. That is right, since they are transformers they stay connected even when you turn your pc or the device off. Using 5-15 watts each 24 hours a day, weather you are using the device or not. With 16 devices each using an average of 10 watts, that is 160 watts an hour! Or 3.8KWh a day, which adds up to some 1400 kWh a year.