Although both USB-C and Thunderbolt are used for power and data transfer, there are some differences between the two. USB-C uses reversible connectors that support both power and data transfer. It has two ends; one end goes into the system, and the other end is not connected to another device for data transfer.
On the other hand, Thunderbolt uses a technology similar to the one used in designing a mini display port of Apple and PCI Express. Thunderbolt seems to be the newest device that enables faster data transfer, developed by both Apple and Intel. Although both devices offer faster data transfer, however, Thunderbolt seems to have more speed compared to USB-C.
For example, the two types of USB-C, USB 3.1 Gen 1 and USB 3.1 Gen 2, offer data transfer with speed up to 5 GB/s and 10 GB/s, respectively. In contrast, the recent Thunderbolt offers a speed of 40 GB/s. Although USB-C supports all devices, a single port of Thunderbolt can be connected up to six devices since most devices that support Thunderbolt come with multiple ports.