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What is USB Power Delivery (USB-C PD)?

In one sentence: The USB-C fast-charging rulebook: the charger and the gadget talk over the cable and agree a voltage and power, from 5 V up to 240 W.

A little more

USB Power Delivery is a set of rules that lets a USB-C charger and a gadget talk to each other through the cable before any fast charging happens. The gadget says what it can take, the charger says what it can give, and they agree a voltage, such as 9 V for a phone or 20 V for a laptop. Until they agree, it stays at a gentle 5 V.

The cable matters too: ordinary USB-C cables carry up to 60 W, and more than that needs a cable with a tiny e-marker chip that tells the charger it can take 100 W or 240 W. If anything in the chain can't keep up, charging falls back to a slower level, which is when laptops show a slow charger warning.

See it in action

  1. BonusWhy do phones and computers get hot?Heat up a pretend phone with games, charging, a duvet or a sunny car, tug a pretend blanket to feel how insulation traps heat, and watch it slow down to protect itself.9 min · interactive

Do it for real

Free grown-up tools and guides on Tooltern, our sister site. They work in your browser and nothing is uploaded.

Related words

  • Watt-hour (Wh) A measure of how much energy a battery holds; unlike mAh it means the same thing for every battery, so it's the fair way to compare a power bank with a phone.
  • Milliamp-hour (mAh) The battery-size number printed on phones and power banks; it counts charge, not energy, so it only compares fairly between batteries at the same voltage.
  • Lithium-ion battery The rechargeable battery in phones, tablets, laptops and electric cars, where lithium ions swim from one side to the other through a jelly as it works.

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