- Definition
- An electronically marked cable, usually called an e-marker cable, contains a small chip that tells the connected devices what current and voltage the cable is rated to carry.
This page defines the term. For what it means in practice, see USB Power Delivery and PPS: how to read a charger specification.
Why a cable needs a chip
A USB-C cable looks identical whether it is built to carry 3 A or 5 A, or to handle the higher voltages of the extended power range. Nothing about the outside of the cable tells the system what it can take.
The e-marker solves that. It is a small integrated circuit in the cable's connector that answers when the source asks what the cable is capable of. The source then limits what it offers accordingly.
What the marking covers
The chip declares the cable's current rating and whether it supports the higher voltages. It may also declare the data capability, which is a separate axis entirely — a cable can be rated for high power and low data speed, or the reverse, and the two are chosen independently.
What it does not cover
An e-marker is a declaration by the cable manufacturer, not a test result. A cable with a chip that overstates its rating will still be treated as capable by the system, and will still heat up if it is not built for the current.
This is why cable quality varies more than charger quality in practice. Chargers are usually tested before they ship, because they carry mains voltage and a certification requirement. A cable often carries no requirement at all, and the e-marker is the manufacturer's own claim.
Practical consequence
When a device charges more slowly than expected, substituting a known-good cable is the fastest diagnostic step available. It isolates the cable from the charger and the device in one action, and cable faults are common enough that the substitution is usually worth doing before anything else.