can some one tell me how you can get 7v from a computer power supply by connecting the 12v+ and 5v+ together and not hurt anything?

 

If they do, it won't be true. You might feed an LM317 with the =12 output and use it to supply the +7.

 

Some say that connecting the load between 12V and 5V terminals gives 7V supply (12-5=7). I wouldn't want to bet on how safe this is, probably will work with small load harmlessly as their grounds are shared. Large load would probably not be safe.

 

It does work the 7V measured it the potential difference.

Regarding safety i'm not sure. People only use this for running there 12V fans at a lower rpm.

Id say its bad practice and not a good permant solution but i have never heard and horror story's on the net because of this ?