When Thunderbolt 3 arrived, it was touted as not only twice as fast as previous generations, but completely backwards compatible with Thunderbolt 1 and 2. Signal-wise, that’s perfectly true. Physically, err... Thunderbolt 3 ditched the previous generation’s mini-DisplayPort connector for the slimmer, trimmer, orientation-agnostic USB Type-C port.
That was a nice move actually, but while adapters for the still plentiful Thunderbolt 2 Macs and perhipherals arrived in short order, they didn’t support bus-power-only devices like all those sexy Thunderbolt portable SSDs I review for Macworld. Bummer.