USB-C Cable eMarker Chips: What They Are and How to Read One

Every high-power or high-speed USB-C cable carries an eMarker chip that declares what it can do. We read the raw chip data off real cables - including a 240W cable that reports USB 2.0 - and show how to check yours on Mac and Windows.

Two USB-C cables can look identical, cost roughly the same, and fit in all the same ports - yet one delivers 240W and the other stops at 60W. One transfers files at 10 Gbps, the other crawls at 480 Mbps. The difference is a small chip embedded in the plug, called an eMarker.

Most explanations of e-markers stop at the theory. This guide goes further: we read the raw chip data off real cables with USB Connection Information and show what they actually declare - including a 240W cable that reports USB 2.0 for data. That single measurement kills the most common misconception about USB-C cables.

What is an eMarker chip?

An electronically marked (“eMarker”, also written e-marker or e marker) cable contains a tiny chip inside the USB-C plug that talks to the host and charger over the cable’s CC (Configuration Channel) wire. Before any serious power or data flows, both ends read a short specification sheet from the chip:

• Maximum current - 3A or 5A
• Maximum voltage - 20V, or up to 50V for Extended Power Range (EPR)
• Maximum data rate - USB 2.0 / 5 Gbps / 10 Gbps / 20 Gbps / 80 Gbps
• Passive or active construction
• Vendor ID of the chip

The charger uses this to decide which Power Delivery profiles to advertise; the host uses it to pick a data rate. A cable without an e-marker is silent, so both ends assume the worst case.

Which cables have an e-marker - and which don’t

This is the part most guides get wrong. A USB-C cable carries an e-marker if it is rated for high speed (above USB 2.0) or high power (above 60W / 3A) - either one, not both.

The cable that came in your phone box almost certainly has no chip in it at all. That isn’t a defect - it’s a cable correctly built to the envelope it was sold for.

What cables without an e-marker can’t do

Any cable charging above 60W must have an e-marker - the specification forbids high current on an unmarked cable for safety reasons. Plug an unmarked cable between a 140W charger and a MacBook Pro 16" and you get 60W, regardless of what either end can do.

What an e-marker actually says - read off real cables

Here’s where theory ends and measurement begins. The chip publishes its specification as a set of 32-bit values called VDOs (Vendor Defined Objects). We read these directly on macOS.

A 240W USB-C cable, measured on 20 July 2026:

ID Header VDO : vendor 0x2095  (CE Link Limited), passive cable
Cable VDO     : 0x110A2640
                bits [2:0]  = 0  -> USB 2.0 (480 Mbps)
                bits [6:5]  = 2  -> 5A
                bits [10:9] = 3  -> 50V maximum (EPR)

Read that again. This is a genuine, spec-compliant 240W cable, and its own chip declares its data capability as 480 Mbps - the same speed as a cable from 2001.

Power and data are independent - the misconception this kills

The single most common assumption about USB-C is that an expensive, high-wattage cable must also be fast. It isn’t. Charging capability and data capability are separate fields in the e-marker, and manufacturers set them independently because copper for power and shielded pairs for high-speed data cost different amounts.

This is not a fringe case. Apple’s own woven USB-C cable, shipped with every iPhone 15 Pro and 16 Pro, is e-marked - and its chip also declares USB 2.0 only. Pair that cable with a Pro iPhone that supports USB 3 and a Thunderbolt Mac and you are still capped at 480 Mbps, because the cable said so.

The e-marker is declarative. The cable’s physical construction might do more, but if the chip says 3A and USB 2.0, that’s the ceiling the whole ecosystem honors.

Practical rule: a wattage number on the packaging tells you nothing whatsoever about transfer speed. If you need both, the packaging has to state both.

Why your computer sometimes can’t read the e-marker at all

This is a trap almost nobody documents, and it will mislead you if you don’t know about it.

We tested one Monoprice cable against two chargers, on the same machine, on the same port, minutes apart:

Same cable. Same port. Same Mac. Opposite results.

The explanation is VCONN ownership. The e-marker chip has no power supply of its own - it runs off VCONN, a small supply on the unused CC pin. Only whichever device is supplying VCONN can address the chip. When you’re charging, roles invert: the charger is in charge and owns VCONN, while your computer is just a sink. Your computer can only interrogate the plug after requesting a VCONN Swap, which is optional in the USB PD specification. A minimal charger simply declines, and your computer has nothing to report.

The consequence matters:

• Over a charge-only connection, “no e-marker detected” means nothing at all. It is not evidence the cable lacks a chip.
• Over a data connection, your computer is the host and owns VCONN by default, so it can always ask. Here, silence genuinely does mean there’s no chip.

USB Connection Information applies exactly this rule: it only claims a cable is limited to 3A when there’s a data connection to justify the conclusion. Any tool that reports “no e-marker” on a charging cable is telling you something it cannot actually know.

The vendor ID names the chip, not the cable brand

When you read a cable’s vendor ID, you are reading the registration of whoever made the chip - not whoever printed their logo on the sleeve.

We measured a Monoprice cable that reports vendor ID 0x291A, which is registered to Anker. The 240W cable above reports 0x2095 - CE Link Limited, a manufacturer whose name appears on no retail packaging anywhere.

Neither is a fault or a counterfeit. White-labeled e-marker silicon is completely ordinary in this industry. Don’t be alarmed when the name doesn’t match the box, and don’t use it to judge authenticity.

Captive cables can’t be read either

A charger with a permanently attached cable - a captive cable - has no plug to interrogate. We confirmed this on a Dell 65W USB-C AC adapter: it published its own identity and negotiated 20V at 3.25A, but exposed no cable data whatsoever.

That combination is itself the signature: identity present, cable data absent, and a contract above 3A. Exceeding 3A normally requires a 5A e-marker to have answered, so if nothing answered and the current is high anyway, the cable is molded in and the rating is built into the charger.

How to check your own cable

On macOS

1. USB Connection Information. Plug the cable in and open the menu bar app. It reads the declared specification directly - speed tier, current rating, passive/active, and EPR voltage - and applies the VCONN rule above so it doesn’t claim more than it can prove.

2. Behavioural test with a high-wattage charger. Connect through the cable in question between a 100W+ charger and a laptop that accepts high-wattage PD. If a 20V / 5A (100W) or higher profile appears, the cable has a 5A e-marker. If the highest is 20V / 3A (60W), it’s unmarked or 3A-rated.

3. Behavioural test for data. Connect a USB 3 device (an external SSD, a Pro iPhone) and read the negotiated speed. 480 Mbps means the cable is USB 2.0 regardless of its power rating. See the cable speed guide.

On Windows

Windows does not expose USB-C cable e-marker data to applications - there’s no equivalent of the macOS interface that publishes it, and Device Manager and USBView show device descriptors, not cable declarations. Reading the chip directly requires a hardware PD analyzer.

So on Windows the practical approach is inference from behavior, which is reliable because the specification is strict about it:

USB Connection Information for Windows reads the negotiated link speed per device from the system tray, which covers the data half of that table live.

Passive vs active cables

Among e-marked cables there’s a second distinction the chip also declares:

• Passive cables are copper plus the chip. At USB4 / Thunderbolt 4 speeds they’re limited to about 1m; longer passive cables drop to 20 Gbps.
• Active cables add signal-boosting chips in each plug and hold 40 Gbps over longer runs (up to 2m for TB4). They cost more and are usually labeled.

For most people a 1m passive Thunderbolt 4 cable is the sweet spot: 40 Gbps and 100W in one cable.

Buying checklist

Match the cable to the job - and remember the two ratings are separate:

• Phone / tablet charging only: any cheap USB 2.0 cable. Save your money.
• MacBook Pro charging (96W / 140W): must be 5A / 100W+ e-marked.
• External SSD at 10 Gbps: a cable that explicitly states 10 Gbps. A wattage claim is not a speed claim.
• Thunderbolt dock / eGPU / dual 4K: a Thunderbolt 4 cable. Undersized cables cause intermittent dropouts and stutter.
• Maximum headroom: Thunderbolt 5 / USB4 v2 (80 Gbps, 240W).

Red flags: “supports fast charging” with no wattage; “charge and sync” with no speed figure; a “100W” cable under about $8 for 1m.

The takeaway

An e-marker is a small chip that declares what a cable can do - and the two things it declares, power and speed, have nothing to do with each other. A 240W cable that runs at 480 Mbps is not broken; it’s a normal product whose chip we read and printed above.

Since you can’t see the chip, the only way to know what a specific cable declares is to plug it in and watch. USB Connection Information surfaces the negotiated data rate and the full PD profile list live on Mac and Windows - so you can tell the cable that earns its price from the one coasting on its packaging.

Related guides

• How to check USB-C cable speed
• Why charging speed and data speed are independent specs
• Why is my device connecting at USB 2.0 speed?
• 100W vs 240W USB-C cables
• Why is my Mac charging slowly? Monitoring USB-C Power Delivery
• USB Reference Guide - versions, connectors, and power

For real-time visibility into other kinds of connections your computer makes, see the rest of the Connection Information suite - audio, displays, and network.