Since87, mate, thanks for your research and the great images.
I wanted to do the same thing, I have the scope but not the two pumps I ordered from Surplus Center.
Anyway, looking at your observations I'm now pretty convinced to use a separate 12V power supply for the pump because:
1. I don't like "pollution" (even negligible) of my Enermax power rails.
2. I still like to be able to run my WC system with the computer PSU powered off (for leak testing etc...)
3. I already have a pump relay for my 220V Eheim 1250, and I can use it with no modifications to switch the Johnson pump together with the Enermax.
An example of a suitable PSU:
The transformer is pretty smal, value of capacitor C1 doesn't bother much, can be any value of some hundreds to thousands of uF, just to smoothen the output voltage a bit.
PS: In case of powering the CO30 by the computer PSU, I still recommend the the "fly wheel" diode on the pump.
When the computer PSU powers down, the pump is still running (slowing down rapidly) and therefore acting as a generator and injecting some voltage back into the PSU.
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