Can I use ATX Power supply without -5 volt out

[jar99]

Can I use an ATX power supply which donot have -5 volt output on a motherboard (Flex ATX form factor) which require -5 volt on pin 18 of ATX power connector.

The reason for doing this is that I want to use DC power supply for my PC but all such DC power supplies do not have -5V output component. I'm unware about the importance of this -5V requirement and is astonished to see it missing in ATX standard power supplies. So can anybody guide me that is it safe to use such power supply?

 

[Nitestick]

i'm not sure how necessary it is but you could do a small mod with a 7905 voltage regulator to create a -5v output if necessary.

 

[jar99]

and what input voltage this voltage regulator requires