How WattageFit decides what limits charging

WattageFit is a supply-side compatibility model: it compares rated limits in the charging path. It does not measure the watts a device is actually drawing.

1. Physical power ceiling

We compare charger power remaining after shared loads, selected-port maximum, cable rating and the preset comparison cap. The lowest value is the available path capacity. This is a rated ceiling, not a live USB-PD measurement.

2. Minimum vs. target

A preset can contain a manufacturer-published minimum charger output and a fast-charge or supply reference. When the manufacturer publishes only a supplied/recommended adapter and no minimum, WattageFit may use a conservative baseline. Estimated values are labeled estimated.

3. Protocol warning

Wattage alone is not enough. If a preset is known to rely on PPS for its advertised fastest charging and you choose plain PD, WattageFit warns that the target speed may not be available. We avoid inventing an exact non-PPS wattage cap unless a primary source provides one.

4. Heavy-load warning

The heavy-load number is a practical reference, not a power-meter reading. If modeled incoming power falls below it, we warn that the battery may drain under sustained load.

5. Cable ratings and current USB-IF markings

For current USB-C to USB-C certification, USB-IF requires 60W or 240W power markings. Older e-marked 5A cables commonly sold as 100W remain in use. WattageFit therefore supports 60W, legacy/common 100W and current 240W/EPR entries, plus manual input. A printed marketing number is not proof of USB-IF certification.

Source policy

Preset priorities: manufacturer specifications and support pages first; standards bodies for protocol/cable behavior. We do not treat retailer listings as authoritative device power sources when a primary source is available.

Important limits

WattageFit cannot inspect USB-PD packets, cable e-markers, battery temperature, firmware behavior or a charger’s hidden power-sharing table from a browser. “Available path capacity” means the rated power the path can support up to the preset comparison target — not the device’s instantaneous draw. WattageFit is not a USB-IF certification check, wattmeter or replacement for manufacturer instructions.

Database reviewed September 12, 2026.