The new USB-C dongle has a traditional HDMI port, a USB-C port and an older full-size USB-A port. It now supports HDMI 2.0, allowing it to output video in 4K at a 60Hz refresh rate with the new adapter when plugged into a 2017 or later iMac, iMac Pro, 15-inch MacBook Pro, last year's iPad Pro or last year's iMac Pro.
Other devices can still output in 4K, but limited to a 30Hz refresh rate.
The update is a modest improvement over Apple's prior dongle, which cost and looked the same but, as Cult of Mac notes, could only output 4K at 30Hz. . While not a major upgrade, the new dongle should help those hoping to make the most of their USB-C machines.