An e-marker, short for electronically marked cable, is a small chip embedded in the plug of some USB-C cables. It stores information such as the cable's maximum current, voltage and, for higher speed cables, its data rate, and reports this to the host and device when the cable is connected.
An e-marker is required for any USB-C cable rated above 3 A, which includes most cables intended for laptop charging or higher wattage Power Delivery, as well as for cables that support USB 3.2 20 Gbit/s or USB4 speeds. A basic charging cable rated at 3 A or below does not need one.
From the outside, an e-marked cable looks the same as any other, so checking the packaging or product listing for its rated wattage and speed is the only reliable way to know what a cable can do. See our guide to USB cables and the entry on active cables for related detail.
