USB Power Delivery, chargers and GaN: charging properly

In short: USB Power Delivery negotiates voltage and current between charger, cable and device (up to 240 W); good chargers with GaN are small and efficient, bad cables and cheap goods are risky.

In more detail: A single USB-C charger can charge smartphone, laptop, Switch and headphones. For that devices agree on suitable values via USB PD.

In Depth

USB PD in brief

• Standard voltages: 5, 9, 15, 20 V (SPR up to 100 W), EPR 28/36/48 V up to 240 W (with 48 V/5 A).
• Negotiation: the charger offers profiles (e.g. 5 V/3 A, 9 V/3 A, 20 V/5 A), the device chooses.
• PPS (programmable power supply): fine-stepped voltage for fast charging (Samsung etc.).
• Wattage = voltage × current (20 V × 3 A = 60 W).
• Fast-charging standards of other manufacturers (Qualcomm QC, proprietary) are partly incompatible, USB PD is the common one.
• A 65 W laptop runs on a 100 W charger (the device draws only what it needs); conversely a 30 W charger charges a 65 W laptop only slowly/not at all.

Cables

• Cables ≥ 3 A (60 W) need an eMarker chip above 3 A (100 W) or 5 A (240 W).
• Data rate (USB 2.0 / 3.2 / USB4/Thunderbolt) and charging power are independent; a thin charging cable often has only USB 2.0.
• Cheap cables without standard can damage devices (wrong resistors); use branded/tested cables.
• Cable quality: length < 1–2 m for 100 W; avoid kinks.
• Plugs: USB-C to USB-A cables (older devices) charge at max. 5 V.

GaN, efficiency and safety

• GaN (gallium nitride): semiconductor allowing higher switching frequencies and less loss → smaller, cooler chargers.
• Marks (CE, VDE/GS/TÜV), reputable manufacturers; no-name power supplies can pose fire/electric shock risk, isolation missing.
• Do not charge covered or on beds; avoid heat.
• Multi-port: power is shared (e.g. 65 W total).
• Standby consumption low; switchable power strip.
• Power banks with PD, flight rules (Wh limit).
• Power supplies for retro devices: often proprietary plugs (barrel, polarity!), see multimeter.

Sparing the battery

• Li-ion likes 20 to 80 % and moderate warmth; permanent full charge in heat ages it.
• Charge limit (80 %) in phone/laptop settings.
• Fast charging occasionally ok; avoid permanent heat.
• Damaged/swollen batteries: do not charge, dispose of properly (hazardous goods, collection point).
• Calibration rarely needed.
• More devices with one charger: worthwhile as a travel kit (GaN 65–100 W + 2 cables).

See also: USB-C, Power bank, Using lithium-ion batteries properly, Power supplies