Counterfeit
How to spot a fake USB-C cable (and what a real e-marker looks like)
· Cablyst
A USB-C cable is not just copper. Any cable rated above 3 A — every 100 W and 240 W cable, every Thunderbolt and USB4 cable — carries a tiny chip called an e-marker that tells the devices on both ends what it can do. Counterfeits lie about what's on that chip. The good news: they lie in predictable ways, and your Mac can read the truth.
The five red flags
- A zeroed or unregistered vendor ID. Genuine cables identify a vendor that is
registered with the USB-IF. A vendor ID of
0x0000, or one that isn't in the registry, is the single most common counterfeit tell. - No USB-IF certification VDO. Certified cables carry a certification data object. Its absence on a cable that claims high wattage or 40 Gbps is a flag.
- Claims the construction can't support. A thin, light cable claiming 240 W is physically implausible — 240 W at 48 V needs real conductors and shielding.
- A price that's too good. A "240 W 40 Gbps" cable for a couple of dollars is almost never what it says it is.
- It gets warm, or runs slower than labelled. Real symptoms of an under-built cable working beyond its actual rating.
What your Mac already knows
macOS negotiates with the cable's e-marker every time you plug in, and exposes the result through IOKit. That's exactly what Cablyst reads: the vendor ID, whether it's registered with the USB-IF, the certification VDO, the current rating, and the negotiated link — then scores the red flags from 0 to 100.
A label is a claim. The e-marker is evidence.
No dongle, no external tester — the data is already on your Mac.
Check yours now
Want a quick gut-check before you install anything? Run the free counterfeit checker — it scores the visible red flags in ten seconds. For the definitive answer, read straight from the hardware with Cablyst Pro.
Want the real, hardware-level answer for your own cable? Install Cablyst or get Pro ($9.99 lifetime).