Hmmm ... the new PSU's should be 24 pin.
The old PSU's were 20 pin.
Anyway you can plug an old 20-pin PSU cable into a new 24-pin MB - they are compatible and won't blow anything up. The connector can only fit one way.
The extra cables are just to supply extra power so the worst that will happen is your MB doesn't get enough juice and you'll get system hanging, freezing, etc.
There are adapters but don't ask me where you'll find one.