Short answer: a USB-C cable from China rated 100W or 5A that fails to deliver 5A, or that overheats at the connector, almost always points to one of three failures: (1) no e-marker chip (the cable silently throttles to 3A), (2) a fake e-marker that returns “5A” to any query but the wire is 28 AWG data-only, or (3) an e-marker chip that was salvaged from a 3A cable and re-marked as 5A. Small importers who only test the visual appearance of the connector miss all three.
Why this problem happens
USB-C cables that carry 5A and 100W under USB Power Delivery must contain an e-marker chip inside one of the two connectors. The e-marker is a tiny EEPROM that responds to USB PD identity queries and tells the host what current and voltage the cable is rated for. A genuine 5A cable carries 5A continuously without overheating because the conductors are typically 20 AWG or 22 AWG and the connector is rated for 5A. A cable marketed as 5A but built with 28 AWG data-only conductors cannot carry 5A without the connector melting.
- No e-marker — the cable works for data and for 3A charging but silently throttles to 3A even when the host and device negotiate 5A. The buyer sees slow charging and assumes the charger is the problem.
- Fake e-marker — a 0-ohm resistor or a salvaged 3A e-marker that returns 5A to any query. The cable negotiates 5A but the conductors overheat. The visible failure is a hot connector or a melted cable jacket.
- Counterfeit USB-IF logo — the cable is printed with the USB-IF certified logo but no TID (Test ID) exists on usb.org for that part number.
China-side explanation
Most USB-C cable factories in Shenzhen run two production lines: a “certified” line with a USB-IF TID and a genuine e-marker chip from a real supplier (STMicroelectronics, Cypress/Infineon, or Weltrend), and a “compatible” line that uses a 3A e-marker or a fake. The “compatible” line is 40 to 60 percent cheaper because the e-marker chip is 0.05 USD vs 0.30 USD for a genuine 5A chip. The wire gauge is also cheaper: 28 AWG data-only vs 20 AWG VBUS for a genuine 5A cable.
The factory does not always volunteer which line the buyer is on. The buyer has to ask for the e-marker chip part number and the USB-IF TID, then verify both on usb.org before paying the deposit. Many factories quote a “5A” cable and ship a “compatible” cable on the second or third reorder, when the buyer has stopped checking.
Step-by-step solution
- Ask the supplier for the e-marker chip part number and supplier. Write the part number on the PO (for example, “STMicroelectronics STM32F072 or equivalent 5A-rated e-marker”).
- Ask for the USB-IF TID (Test ID) of the cable. The TID is a 6 to 8 digit number issued by USB-IF after the cable passes compliance testing. Look it up at usb.org.
- On a 5-piece sample, measure end-to-end resistance from USB-C plug pin to USB-C plug pin with a digital multimeter. A genuine 5A cable measures 50 to 150 milliohm per conductor (depending on length). A 28 AWG data-only cable measures 250 to 500 milliohm per conductor.
- Run a 5A load test for 10 minutes using a USB-PD trigger set to 20V/5A and an inline wattmeter. A genuine cable holds 100W without overheating; a fake cable drops below 60W within 2 minutes and the connector becomes too hot to touch.
- Use a USB-C cable tester (30 to 100 USD) to read the e-marker identity. A genuine 5A cable returns current=5A, voltage=20V, and cable type=Passive 5A. A fake or missing e-marker returns nothing or returns a 3A rating.
- Inspect the USB-IF logo on the housing. A genuine logo is embossed or laser-etched; a counterfeit is printed. The TID must be printed near the logo per USB-IF trademark rules.
- Lock the e-marker part number, USB-IF TID, end-to-end resistance limit (e.g. less than 200 milliohm), and 5A load test pass on the PO. Reject any shipment that does not match.
What to ask the supplier (copy-paste)
"Please confirm in writing: (1) e-marker chip part number and supplier (must be a 5A-rated chip, not a 3A chip relabelled), (2) USB-IF TID for the cable, (3) conductor gauge for VBUS and GND (must be 20 AWG or 22 AWG for 5A, not 28 AWG), (4) cable length and rated voltage / current, (5) 5-piece pre-shipment sample so I can run end-to-end resistance test, 5A load test, and e-marker read with a USB-C tester, (6) USB-IF logo format and TID printed on the cable per USB-IF trademark rules."
Risk matrix
| Failure mode | What controls it | Buyer check |
|---|---|---|
| No e-marker (3A throttle) | E-marker chip present | USB-C tester e-marker read |
| Fake e-marker (overheat at 5A) | Conductor gauge + chip part | End-to-end resistance + 5A load test |
| Counterfeit USB-IF logo | USB-IF TID on file | Lookup TID on usb.org |
| Salvaged 3A e-marker | Chip part number on PO | Visual inspection under magnifier + part number trace |
Buyer checklist before signing the PO
- E-marker chip part number on PO (must be 5A-rated).
- USB-IF TID declared and resolvable on usb.org.
- Conductor gauge for VBUS / GND declared (20 or 22 AWG).
- Cable length and rated voltage / current on PO.
- Pre-shipment 5-piece sample approved.
- End-to-end resistance less than 200 milliohm per conductor.
- 5A load test for 10 minutes passed without overheating.
- USB-C tester e-marker read returns 5A rating.
- USB-IF logo format and TID printed per USB-IF trademark rules.
Authoritative references
- USB-IF — USB Power Delivery specification and charger compliance
- USB-IF — certified logo trademark and TID lookup
- USB Type-C Cable and Connector Specification Release 2.3
- IEEE Standards Association — general standards framework
- IEC — International Electrotechnical Commission
- QIMA — pre-shipment inspection and supplier verification
USB-C 5A / 100W capability is governed by the USB Type-C Cable and Connector Specification Release 2.3 and the USB Power Delivery specification. The USB-IF TID database is the public reference for genuine certified cables. This article is a sourcing verification checklist, not electrical safety legal advice. Confirm current requirements with USB-IF or a licensed testing lab before placing the bulk order.