Are all USB-C cables the same? What the e-marker chip does

What an e-marker is

The USB Type-C specification defines an eMarker as the element in an electronically marked cable that returns information about the cable in response to a USB Power Delivery command. It gives the example of the cable's current-carrying capability, its performance and its vendor.

Microchip's guide lists what that identity can contain, including the vendor and product IDs, hardware and firmware revisions, the cable's current capability of 3 A or 5 A, and its data signalling capability. The chip is generally powered through a dedicated line in the cable called VCONN.

Which cables have one

Not all of them, and that is by design. In the 2019 release of the Type-C specification, all full-featured USB Type-C cables must be electronically marked, while USB 2.0 Type-C cables may be. Microchip's guide adds that active cables, which contain signal conditioning electronics, and cables supporting more than 3 A are required to include one.

What happens without one

Before it negotiates power, a USB PD charger can send the cable a Discover Identity message. If there is no marker or no response, the Type-C rules, as Microchip describes them, say the cable must be assumed to carry no more than 3 A. A port able to supply more has to confirm a 5 A rating first, and only then offers more than 3 A to the device at the other end.

At the top of the standard range, 20 V at 3 A is 60 W. So a 100 W charger and a 100 W laptop joined by a cable that reports no 5 A rating have 60 W to work with. The guide to USB-C Power Delivery explains that negotiation in full.

Power and data are separate

A high wattage does not mean high speed. USB-IF's logo guidelines say USB 2.0 Type-C 60W and 240W cables deliver data at up to 480 Mbps. A cable could therefore be rated for a laptop's full power and still be slow for moving files, so check both figures if you care about both.

How to read the label

USB-IF runs a logo programme for certified cables. Its January 2026 guidelines say USB-C to USB-C cables going through the compliance programme must be labelled on the cable itself, embossed or printed on the overmold, with the appropriate data rate and power wattage logo. Its example is a 20 Gbps cable supporting 20 V at 3 A, which carries a combined 20Gbps/60W logo.

Those logos are for products that have passed USB-IF's compliance testing. A cable without one has not shown you that it has. The e-marker itself cannot be seen from the outside, so a seller's description is not proof of what is inside.

Which cable you need

• Most phonesApple asks for a USB-C cable compliant with the USB-C standard, such as the one that comes with an iPhone. For the fastest charging on iPhone 18 Pro models and iPhone Duo, Apple's notes specify a 60W-capable cable.
• A laptop on over 60 WLook for a 5 A rating up to 100 W, or a 240W logo above that. Texas Instruments lists a 5 A cable as required above 60 W and an EPR cable as required above 100 W.
• Moving files or running a displayCheck the data rate on the cable as well as the wattage.