I have two +12 V smps which are identical.They have com,ground,+v terminals.
how can I get -12v/+12 using these smps.Sorry for this stupid question but my I can not come up with a solution.
On one SMPS have ground connected to +, it will be a negative power supply. On the other SMPS have ground connected to -, it will be the positive power supply. Use the grounds on the SMPS terminals.
Then connect the grounds together.
I am assuming com is the - terminal, and it is not already connected to ground. Please post the datasheets for the power supplies.
Most good power supplies are floating. Ones like the old HP brands had a jumper that could connect their ground to either the plus or minus jacks. The really good ones have voltage sense lines that let you regulate the voltage at the point of use.