Nominal primary voltage on transformers

A quick search on power supply, bench pc, computer etc will show you that your quest is a popular one.

Do some research and reading before soldering.

and keep asking questions.

I like to think I have more confidence in university graduates tobe than DonQ appears to have.

Here are some old threads to get you going.

http://forum.allaboutcircuits.com/showthread.php?t=21587

http://forum.allaboutcircuits.com/showthread.php?t=15793

http://forum.allaboutcircuits.com/showthread.php?t=13031

http://forum.allaboutcircuits.com/showthread.php?t=7117