GTrusted

To use pre-Thunderbolt 3 peripherals like the LaCie Rugged Thunderbolt External Hard Drive (USB 3.0) on the Dell XPS 15 9550, one needs special adapters like the StarTech Thunderbolt 3 to Thunderbolt Adapter.

When you plug the StarTech Thunderbolt 3 to Thunderbolt Adapter into the Thunderbolt 3 port of the Dell XPS 15 9550, a message window pops up on the bottom right corner of your screen, telling you to approve the Thunderbolt device before use. Note, you will see the Thunderbolt device that is connected to the StarTech Thunderbolt 3 to Thunderbolt Adapter as the device that needs to be approved (and not the adapter itself).

After selecting 'Always Connect" in the Approve Thunderbolt Devices window, you can see the LaCie Rugged Thunderbolt External Hard Drive (USB 3.0) show up as a new drive on Windows.

In the Windows Device Manager, we can also confirm the LaCie Rugged Thunderbolt External Hard Drive (USB 3.0) enumerates as a SATA AHCI Controller within the PCI Express Root Complex.

We can also confirm that file transfers are working well.

Like with any other drive, you can also safely eject the LaCie Rugged Thunderbolt External Hard Drive (USB 3.0) from the Dell XPS 15 9550.

StarTech Thunderbolt 3 to Thunderbolt Adapter works well with the Dell XPS 15 9550, allowing it to connect to pre-Thunderbolt 3 peripherals like the LaCie Rugged Thunderbolt External Hard Drive (USB 3.0).