What is USB-C and why are not all USB-C cables the same?
USB-C describes only the physical connector, not what the cable can do. That single fact explains almost all the confusion, because two cables that look identical and fit the same ports can differ enormously in capability.
Three things vary independently.
- Data speed. Some cables carry only the slowest data rates, while others support successive faster standards, and the fastest also carry video. A cable supplied with a phone is frequently among the slowest, which is fine for charging and painfully slow for transferring files from a camera or drive.
- Power. Cables are rated for how much current they can carry, and a cable rated for a phone will not safely deliver what a laptop requires. Higher wattage cables contain a chip that reports their rating so the devices negotiate appropriately.
- Alternate modes. Carrying video output or supporting Thunderbolt requires additional wiring that many cables do not have. A monitor that will not display over a cable that charges fine is almost always this.
The worst case in practice is a charge-only cable with no data lines at all, common with inexpensive accessories, which makes a device charge normally while never appearing on a computer.
Because none of this is visible, the practical guidance is to keep good cables and label them, buy from reputable brands where the specification is stated, and avoid assuming a cable that came with one device suits another.
Thunderbolt cables are the safe default when you want one that does everything, since they support the highest data rates, video and full power delivery, at the cost of being more expensive than most situations require.