Why is my MacBook charging so slow? A real diagnosis.

In macOS Tahoe 26.4, Apple added a "Slow Charger" label. Plug in a charger that can't deliver full power and the menu bar tells you so. What it doesn't tell you is why. That's the gap. The OS confirms what you already suspected (yes, it's charging slowly) and then leaves you to guess whether the problem is the adapter, the cable, the port, the battery, or the laptop itself. Most of the time it's…