The cable can connect a 2.5' or 3.5' SATA hard disk drive (HDD) externally to any available Power eSATA port. Does not require any additional power supply for a 2.5' or 3.5' SATA hard disk drive (HDD). Power Over eSATA port combines eSATA and USB and enables, by help of the two gold contacts, a power supply of 12 V. Currently, most computer motherboards support 5V power supply, which is suitable for 2.5-inch hard disks with a rated voltage of 5V. If you connect a 3.5-inch hard disk, please confirm whether the motherboard supports 12V voltage output.