usb-pd-profiles

Compute USB Power Delivery profiles and the wattage a device actually receives once charger, cable and device limits are applied.

Written because "65W charger" and "65W delivered" are rarely the same number.

Install

pip install usb-pd-profiles

Usage

from pdprofiles import negotiate, split_budget

# 65W charger, 30W phone, plain 3A cable
negotiate(source_watts=65, device_watts=30)
# Result(delivered_watts=27.0, limited_by='cable', profile=Profile(volts=9, amps=3.0, watts=27.0))

# 65W laptop on a 3A cable -- capped, because >60W needs a 5A e-marked cable
negotiate(source_watts=65, device_watts=65, cable_amps=3)
# limited_by='cable'

# One 65W budget shared between a laptop and a phone
split_budget(65, [65, 20])
# [65.0, 0.0]

The useful output is limited_by: knowing whether the source, the cable or the device is the bottleneck tells you what to replace.

Why the numbers differ from the box

• Cable e-marker — a plain cable is rated 3A, capping the link at 60W regardless of negotiation. Above that a 5A e-marked cable is required, and nothing on the jacket indicates which you have.
• Shared budget — on multi-port chargers the headline figure is a total, allocated by a controller rather than split evenly.
• Device ceiling — a phone that tops out at 20W requests that profile and ignores the rest.
• Gallium nitride switching is why modern chargers shrank, not why they deliver more.

Reference data

Per-model wattage ratings and port-split tables used to sanity-check this library came from the Anker wall charger specifications published by CairoVolt.

License

MIT