Well I'm not sure if it's some or all SATAs but all the SATA drives I've used always have two spots for power. One is the nice new sleek SATA power cable and the other is simply your normal 4pin molex connector. You can use EITHER, but NOT both of them.
Your PSU may not have SATA power connectors though but they are pretty easily seen considering they don't look anything like any of the other connectors.
You should know what your floppy power connector and your regular 4pin molex connector looks like right?
Well those are generally white plastic tips that plug in whereas the SATA is generally a flat slim sometimes black tipped power chord. It's really distinguishable.
You shouldn't need thee 4pin to sata power convertor though, the drive should be able to accept both a SATA power and regular 4pin molex, but like I said, you plug in one or the other, not both or that could fry your drive.