Hi
2.5" hard drives only need 5 volt power but 3.5" hard drives also need 12volts
For the motor circuits
USB ports can provide 5v 0.5 amp for most 2.5" drives , some require two USB plugs one for power & data and another for power only, useful for drives needing more than 0.5 amps
( I was referring to USB 1 & USB 2 not USB 3 which provides 5 v but more current (power is available)
Regards
Mike Barnes