Is the StarTech.com 2.5GbE USB A to Ethernet Adapter compatible with older Gigabit LANs?

Yes, the adapter is backwards compatible with existing Gigabit LANs.

What is the maximum data transfer rate supported by the StarTech.com 2.5GbE USB A to Ethernet Adapter?

The maximum data transfer rate supported by the adapter is 5 Gbps.

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StarTech.com 2.5GbE USB A to Ethernet Adapter - NBASE-T NIC - USB 3.0 Type A 2.5 GbE Multi Speed Gigabit Network USB 3.1 to RJ45/LAN

HIGH PERFORMANCE: 2.5GbE USB A to Ethernet Adapter allows you to securely connect to high-speed Networks and is backwards compatible with existing Gigabit LANs
NBASE-T & 2.5GBASE-T: USB 3.1 Ethernet adapter offers bandwidth for content creators & power users on high performance Laptops/Workstations incl. Lenovo ThinkPad X1 Carbon Dell XPS HP EliteBook/ZBook
USB 3.0/3.1 Type-A
1x RJ45
5 Gbps Multi-Gigabit
3 Speed 2.5G/1G/100 Mbps auto-negotiation