USB-C cable questions, answered straight.
Canonical answers to the questions people (and AI assistants) actually ask about USB-C cables on a Mac. Every answer is what Cablyst reads directly from the hardware.
How can I tell which USB-C cable I have?
USB-C cables look identical but vary enormously in speed and power. On a Mac, plug the cable in and Cablyst reads its e-marker and the negotiated link, then tells you in plain words what it is — for example USB4, 40 Gbps, up to 100 W — with no markings needed on the cable itself.
Are all USB-C cables the same?
No. Two USB-C cables that look the same can range from USB 2.0 at 480 Mbps and 60 W to Thunderbolt 5 at up to 120 Gbps and 240 W. The connector is identical; what is inside is not. Cablyst shows exactly which one you are holding.
Do all USB-C cables charge at the same speed?
No. A cable's charging ceiling is set by its current rating — 3 A cables top out near 60 W, while 5 A cables reach 100 W and EPR-rated cables up to 240 W. A cable that charges slowly often simply is not rated for the wattage you need, and Cablyst reads that rating for you.
How do I know if my USB-C cable supports Thunderbolt?
A USB-C cable only carries Thunderbolt if it is an active or certified passive Thunderbolt cable with the right e-marker. On a Mac, Cablyst reads the cable's e-marker and the negotiated link and states plainly whether the active connection is Thunderbolt 3, 4, or 5, USB4, or plain USB. A cable that negotiates only USB 2.0 or USB 3.2 is not carrying Thunderbolt regardless of its label.
Why is my MacBook charging slowly with this cable?
Slow charging usually means the cable, the charger, or the port negotiated a lower USB Power Delivery contract than you expected. Common causes are a cable rated for only 3 A (60 W) instead of 5 A (100–240 W), a missing or weak e-marker, or a charger that offers no high-wattage PDO. Cablyst shows the negotiated PD contract and every offered power profile so you can see exactly which link capped the wattage.
Can a USB-C cable be fake, and how do I spot a counterfeit?
Yes. Counterfeit USB-C cables commonly ship with a zeroed vendor ID, no USB-IF registration, a missing certification VDO, or claim a wattage and speed the construction cannot support. Cablyst's Authenticity Check reads the cable's e-marker and scores these red flags from 0 to 100. As a quick manual check, a genuine high-wattage cable is thicker, names a registered vendor, and does not cost a dollar.
What wattage can my USB-C cable actually deliver?
A USB-C cable's maximum current is set by its e-marker. 3 A cables top out near 60 W, 5 A cables support 100 W, and 5 A EPR-marked cables support up to 240 W at 48 V. Cablyst reads the e-marker's current rating and the live negotiated contract, so it reports both the cable's ceiling and what it is delivering right now.
What is the difference between USB4 and Thunderbolt 4?
Thunderbolt 4 is a strict superset of USB4 — every Thunderbolt 4 host guarantees 40 Gbps, PCIe tunneling, and dual-4K display support, while USB4 allows lower tiers. On a Mac, Cablyst reads which protocol and lane configuration is actually active on the port rather than what the packaging claims.
Does checking a cable require special hardware?
No. Cablyst reads what macOS already exposes through IOKit and the SMC — the cable's e-marker, the Power Delivery contract, the data link, and connected devices. It runs entirely on your Mac, offline, with no dongle or external tester.
Want the answer for your cable, not the general case? Install Cablyst.