Can i connect two computer power supplies in parallel to get high current?

i need 12 volt 25A output.

 

You really shouldn't do that. The supplies will "fight" each other.

Here's a 600W ATX supply you could convert to a bench supply:
http://www.mpja.com/email/02-23-10a.asp?r=%%ref%%&s=2
12V@27A, $19.
No need to parallel; one's enough.

 

Connect the grounds together. Put a .1 ohm resistor in series with each +12 volt ouput and put them in parallel. When you draw 10 amp from each there will be a 1 volt drop across the resistor. ( and 10 watts of waste heat ). This will encourage load sharing and decrease the tendency to "fight". It will compensate for some voltage mismatch of the output voltages, but at the cost of waste heat and poor load regulation.