My laptop charges from every USB-C cable except the one in my travel bag

I thought USB-C had finally reduced my cable problem. One shape, several devices, less rummaging. Then my laptop battery fell to 6 percent in an airport while it was visibly connected to a charger.

The charging symbol appeared, but the battery kept dropping during a video call. The same charger fills my phone quickly. The same laptop charges normally at home. The cable in my travel bag looks almost identical to the cable on my desk, so I had treated them as interchangeable.

After the call, I shut the laptop and the percentage began rising slowly. That suggests the setup was providing some power, just not enough for the laptop's workload. I do not yet know whether the limit is the wall adapter, the cable, the outlet, or the way the laptop negotiates power.

I have labeled the known-good home pair and stopped mixing parts while testing. My plan is to compare the travel cable with the home adapter, then the travel adapter with the known-good cable, while the laptop is idle. I will use the specifications printed on the equipment and the laptop maker's requirements rather than guessing from connector shape. I will not buy a bag of unverified “fast” cables and hope one is lucky.

The broader lesson is irritating: a shared connector does not make every cable and power source equivalent. The convenience is real, but the capability is not visible from across a room.

How do you label and test USB-C gear without becoming the person who carries a spreadsheet for cables? I want a simple travel system that tells me which combination can actually support the laptop, not merely make the charging icon appear.