I'm looking at purchasing a 2.5" hard drive and an external enclosure. The main feature i want is not having to use an AC adapter or a second USB port to power the drive. Is there any evidence or research done to tell us, say that 5400 vs 7200rpm hard-drives require less power, so they don't need a secondary power supply? For example, most 2.5" external hard-drives, like the WD Passport series, only require the 1 USB connection for power and data. How do i mimic this single USB connection with a bare-bone 2.5" drive and an aftermarket 2.5" enclosure?? Much Thanks!!