GUIDE: How to check for unsafe USB-C Vbus HOT devices and chargers. Or, how to "make it safe" yourself.
(An in-depth analysis WHY can be found in the linked sister post.)

This article has been split into two for clarity. See the companion article expaining WHY here:


Please look at the images provided. (Photos courtesy of +Jason chapman.) This is shows an unsafe #USB #TypeC Tronsmart W2PTE charger which has Vbus HOT. (The W2PTU is too.)

Method 1: LED
The quickest, simplest, and least dangerous way to test (only risks hurting the charger or a cable) is to shove an LED in the Male-A port of an A-to-C cable connected to the charger. That is pictured here:

*EDIT (8/3): * So you don't burn out your LED, please twist a 330 ohm to 5k ohm resistor onto one leg of the LED so it doesn't get overloaded.

Method 2: USB hub
The second easiest way involves using a cheap USB hub (not computer/device) .
(1) Unplug everything *FIRST!*
(2) Connect the USB-C output of the charger to the C-end of an male A-to-C "Legacy Host Adapter" cord
(3) Connect the USB-A end of the A-to-C cord to a downstream port of a USB-A hub that isn't connected to anything
(4) Plug the USB-C charger into the wall and look for changes in the USB-A hub/charger
If the USB-A hub lights up, the charger indicates it is delivering power, or you hear buzzing sounds your adapter [or cable!] is Vbus HOT and unsafe. It won't explode, but it is unsafe and does mean you can potentially damage things a number of ways. (See the second image for some gore.)

Method 3: Multimeter [Experts only, 3A short risk]
Another method to test if you have a multimeter is to measure either (a) the 2 outermost pins on the USB-A male plug or (b) the rightmost pin [facing the plug] and the metal shield. 0v good, 5v bad. Please be careful not to short out the probe against the shell!

Below are all the classes of devices that can potentially result in (unsafe) Vbus HOT scenarios:

- Chargers with QC 3.0 on USB-C
They may have "recycled" a circuit from Type-A QC3.0 charger where Vbus HOT is legal and allowed. Or may be implemented poorly, as I discovered in a previous analysis. 'Corner case' here:
- Noncompliant charger with Vbus HOT, without CC-based switching
- unsafe A-to-C cable
A miswired male A-to-C cord with a (5.1kR Rd pullDOWN) instead of an (56kR Rp pullUP) can cause this exact same behavior. It has happened before. See below.
Or, it can be an "degenerate A-to-A" cable. Degenerate means "works exactly like __". It doesn't have to be an actual A-A cable. You could "build your own" with unsafe adapters!
- Adapter lacking Class II/Double Insulation certification
(Here I refer to the cheapest-of-the-cheap unregulated adapters. RUN, don't walk, away.)


(A) Please contact the manufacturer or place of purchase and ask for a replacement that complies with USB-C Specification 1.2 regulations on Vbus switching HOT/COLD per [Section 4.4.2 VBUS]:

"The Source’s USB Type-C receptacle VBUS pin shall remain unpowered (...) until a Sink is attached. The VBUS pin shall return to the unpowered state when the Sink is detached."

(B) The *ONE* exception to the Vbus HOT rules are captive cable "dumb" chargers. (No USB-PD!) This is because it is impossible to plug a male USB-C end into anything else by accident. [Section USB-based Chargers with USB Type-C Captive Cables]:

"A USB-based charger with a USB Type-C captive cable that does not support USB PD may supply VBUS at any time. It is recommended that such a charger only apply power to VBUS when it detects a Sink is present and remove power from VBUS when it detects the Sink is not present"

So by taking a USB2.0 NON-eMarked C-C cord, and permanently epoxying it to the face of the charger, you will now be "effectively" safe! (I say non-eMarked because of possible technical issues related to this article here:)

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