I read the hidden chip inside my USB-C cables, and the packaging was lying

I expected the chip inside the Portronics Flash C2 to contradict its own box. The box says "Thunderbolt 4.0," and I assumed the tiny e-marker in its USB-C plug would admit to something slower. Instead, my M2 MacBook Air read it with a Samsung T7 Shield on the far end and a free app called WhatCable, and the chip agreed: USB4, 40Gbps, 240W.

The giveaway came from Portronics' Konnect 240C, a USB 2.0 charging cable that costs under $4. Its chip reports the same blank identity with three bits changed. Thunderbolt 4 requires certification, and nothing on the Flash C2 has it. The box was lying, and the chip happily repeated it.

How to read the e-marker chip in a USB-C cable

A free app, one command, and a drive on the far end

Every USB-C cable rated above 3A, and every 40Gbps cable, carries one of these chips, called an e-marker. It stores a few numbers: the cable's top data speed, the current it can handle, its maximum voltage, and who made it. Your laptop reads them at every plug-in and decides how hard to push the cable.

On Apple Silicon Macs, those numbers land in the system registry, and WhatCable turns them into plain English from the menu bar. It's free and open source, and one Terminal command installs it: brew install --cask darrylmorley/whatcable/whatcable. If you'd rather see the raw data, ioreg -r -w0 -c IOPortTransportComponentCCUSBPDSOPp prints exactly what the chip said.

There's one catch. The chip only answers when a device sits on the far end, because the laptop doesn't power it until it sees something there. My T7 Shield did that job for all three cables. I'll admit I wanted the Flash C2's chip to snitch on its box. It didn't: WhatCable reported USB4 Gen 3 at 40 Gbps, rated for 50V at 5A, which works out to 240W.

The Mac measured 10 Gbps, but that's the T7 Shield's own ceiling, and WhatCable says as much. So the chip's 40Gbps stays a claim here. Only a Thunderbolt or USB4 drive or dock on the far end would show the real link speed.

WhatCable only runs on Macs. On Windows, a USB-C meter that reads e-markers, such as ChargerLAB's Power-Z KM003C, shows the same chip data when you plug the cable into it.

The other two cables told the truth

Including the one with no chip at all

The Konnect 240C never claimed to be fast. Its box promises 240W and an "E-Marker Chipset," and Portronics' own listing calls it a USB 2.0 cable. Its chip agreed on every count: USB 2.0, 5A, 50V, 240W. The T7 Shield crawled at 480 Mbps through it, exactly as labeled.

Samsung's short cable from the T7 Shield box is even plainer. No chip answered at all, and the Mac still ran the drive at its full 10 Gbps. A laptop treats a cable without an e-marker as a 3A, 60W cable, which matters when you're charging something hungry and doesn't matter one bit for an SSD.

So two of my three cables matched their packaging. The third matched its packaging a little too well.

How a USB-C e-marker can claim speeds it never proves

The chips are basically twins

Each chip answers with four 32-bit values: an ID header, a certification ID, a product ID, and a cable record with the speed and power ratings. Here are both Portronics cables, straight from Terminal:

Flash C2: ,,,

Konnect 240C: ,,,

macOS prints the bytes in reverse, so the interesting part sits in the first two characters of each value. In the cable record, 40 becomes 43, which moves the speed field from USB 2.0 to USB4 Gen 3. In the ID header, 18 becomes 1c, which sets the flag a cable uses to say it supports extra modes, the way Thunderbolt cables introduce themselves. That's three bits out of 128.

Everything else is identical. Both chips report a vendor ID of zero, a certification ID of zero, and a product ID of zero. They even claim the same length class, roughly two meters, for cables Portronics sells at 1.2 and 1.25 meters. I laughed out loud at that point, which isn't a normal reaction to hex.

An e-marker isn't a test. It's a tiny chip that a factory programs, and it reports whatever someone wrote into it. WhatCable's own documentation says it shows the chip's claim, not what the wiring can carry. A blank vendor ID alone proves nothing, since plenty of genuine cables ship that way. A Thunderbolt cable whose chip is a near-copy of a USB 2.0 charging cable's is a different story.

Thunderbolt 4 is a certification, and this cable never got one

Check the plug, the logo, and Intel's directory

Thunderbolt isn't a speed you can print on a box. Intel's own messaging guide lists "mandatory certification for all shipping computers, accessories, and cables," and certified products appear in Intel's Thunderbolt product directory. Portronics isn't in that directory's company list, and its chip reports no maker and no certification ID.

The cable doesn't play along either. Its plugs are etched with "USB4.0" and "240W 40Gbps 8K60Hz," and neither plug carries a Thunderbolt mark. The box calls it "Thunderbolt 4.0," a version name Intel doesn't use. It can't even agree with Portronics' website: the box says 1.25 meters and cotton braiding, while the listing says 1 meter and nylon.

To be fair, none of this proves the Flash C2 can't reach 40 Gbps, since some uncertified USB4 cables do. It ran my T7 Shield at full speed, and its charging speeds matched the box when I tested it earlier with a USB-C meter. It's a decent cable for about $10, wearing a Thunderbolt costume.

I'm keeping it, just not for Thunderbolt

The Flash C2 stays in my bag as a charging and SSD cable. The Konnect 240C stays on charging duty. For a Thunderbolt dock, I'd only buy a cable with the logo on its plug and a listing in Intel's directory. Before I trust another USB-C cable, I'll spend two minutes with WhatCable and a drive on the far end. It can't tell you what the copper can do. It shows you exactly what someone wanted the chip to say.