Is this adapter compatible with Mac OS and Linux operating systems, or is it only for Windows?

The adapter is compatible with Mac OS.

Will this adapter require an external power source when connecting a 3.5" HDD, or is power supplied through the USB connection?

The adapter requires a 12V/2A power adapter when connecting a 3.5'' HDD.

Does this adapter support data transfer speeds up to 6 Gbps with SATA III drives?

Yes, this adapter supports data transfer speeds up to 6 Gbps with SATA III drives.

Questions & Answers: LUOM USB 3.0 To Sata 3 2 1 HDD SSD Hard Disk Drive Adapter Converter Cable SataIII To USB 3.0 for 2.5" 3.5" Inch Sata III II I, Compatiable for WD, Seagate, Toshiba, Samsung, Hitachi-Black

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LUOM USB 3.0 To Sata 3 2 1 HDD SSD Hard Disk Drive Adapter Converter Cable SataIII To USB 3.0 for 2.5" 3.5" Inch Sata III II I, Compatiable for WD, Seagate, Toshiba, Samsung, Hitachi-Black

Features:
Adpter SATA III USB 3.0 Cable External Hard Drive USB to Serial ATA 22pin Converter Hard Disk 6 Gbps for 2.5"""" and 3.5"""" HDD/SSD.
This USB 3.0 to SATA Converter Cable connects any standard 2.5 or 3.5 inch SATA Hard Drive or Solid State Drive (SSD) to a computer through USB 3.0 ports. It's a ideal for you to backup files or upgrade your notebook hard driver.
Easy and quick access to external storage;
Fully compatible with USB 3.0 and backwards compatible with USB 2.0/1.1;
Plug and play,hot-swapping;
Comply with serial ATA2.0 standards.
Compatible with USB port (1.0,1.1 &2.0) & SATA Hard disk (1.5 GB/S & 3 GB/s).
Wide Compatibility
* Compatible with 2.5 ''/3.5 '' HDD, SSD.
* Compatible with Windows 98, 2000, XP, Vista, 7, 8, 10 and Mac OS X.
* Compatible with PS4, connecting 2.5 ''/3.5 '' HDD working as a expansion. Note: Please connect 12V/2A power adapter for 2.5 ''/3.5 '' HDD

$21^.49 –