[tw04]

>but how do you distinguish a Thunderbolt-compliant cable from a very basic USB-C cable?

The picture on the end of the cable - it will contain a picture of a lightning bolt, and a number indicating which version of thunderbolt the cable supports:

https://www.thunderbolttechnology.net/sites/default/files/CB...

[listenallyall]

I don't think it is as easy as you imply...

Belkin's Thunderbolt 3 cable supports 60W power delivery https://www.belkin.com/thunderbolt-3-cable-usb-c-to-usb-c-3....

Cables 2 Go's Thunderbolt 3 cable supports 100W https://www.cablestogo.com/usb-and-pc/usb-c-cables-adapters-...

StarTech says optical Thunderbolt 3 cables don't support power delivery at all https://www.startech.com/en-us/faq/thunderbolt-3-power-deliv...

[pchangr]

Thunderbolt 3 has to give up to 15 watts of power delivery on copper cables, anything beyond that is out of scope for the standard.