Instructables

Essential Benchtop Lab SMPS from a Computer SMPS

Step 5: Mount the Header Board

Remember that whole metal or aluminum case of the SMPS is Ground/GND/Earth or whatever you call it.

So make sure that no +5 or +12 or +3.3V or -12V pin touches it.
That's why I have used long nuts to keep proper spacing.
Its totally fine if these nuts are tightened with screws on GND pad of the PCB.