Originally Posted by TIGR
Can someone who understands the laws governing electricity better than I do, explain whether or not this can be safely done, why, and from where the 2.4a of the six fans will be drawn if powered between the +12v and -12v rails?
You need to understand that to get 24V from the +12v and -12v you need to wire them in series (one after another).
When in series, the current flowing through the wire loop (psu->fan->psu) is the same at all points. So in your case the 2.4A is required for the fans, so 2.4A is going through the -12V and the +12V.
This excedes the limit for your power supply as you mentioned it was less than 1A. Bet case scenario, you connect it up and the PSU may shut off, or something.. worst case you could damage it.
As for the general topic here on overvolting fans... (and as some people have found). The fans could run faster when overvolted, but you are more likely to melt the windings in the motor, or destory the circuits on the fan (PWM fans for example have control circuits as well). Still fun to try if you don't care about the fan lol.