USB Power Delivery Explained: A Complete Technical Guide

The Evolution of USB Charging

USB charging has come a long way from the humble 500mA (2.5W) of USB 2.0. Those early standards were designed for data transfer with charging as an afterthought. As smartphones became more powerful and batteries grew larger, the need for faster charging became critical.

Various proprietary solutions emerged—Qualcomm Quick Charge, Samsung Adaptive Fast Charging, OnePlus Warp Charge, and others. Each offered faster charging but only within their ecosystems. This fragmentation frustrated consumers who needed different chargers for different devices.

USB Power Delivery (USB PD) emerged as the universal solution. Developed by the USB Implementers Forum (USB-IF), USB PD provides a standardised, open protocol for high-power charging that any manufacturer can implement without licensing fees.

Key Point: USB PD is a protocol (a way of communicating), not a hardware type. It works over USB-C cables and can deliver up to 240W with the latest specifications.

How USB PD Negotiation Works

When you connect your device to a USB PD charger, an elaborate negotiation occurs in milliseconds. Understanding this process helps explain why certain charger-device combinations work better than others.

The Communication Process

1. Detection: The charger detects a device connection and begins the handshake process

2. Source Capabilities: The charger sends its available power profiles to the device

3. Request: The device evaluates options and requests its preferred profile

4. Acceptance: The charger confirms it can supply the requested power

5. Power Delivery: The charger adjusts to the agreed voltage and current

This negotiation happens via a dedicated channel called Configuration Channel (CC) in the USB-C connector. It's completely separate from data transfer, ensuring power negotiation never interferes with other USB functions.

Power Data Objects (PDOs)

Chargers advertise their capabilities through Power Data Objects. Each PDO specifies:

Voltage level (5V, 9V, 15V, 20V, or custom voltages with PPS)
Maximum current at that voltage
Whether the source supports variable voltage (PPS)

A typical 65W charger might advertise these PDOs:

5V at 3A (15W)
9V at 3A (27W)
15V at 3A (45W)
20V at 3.25A (65W)

Your device reads these options and selects the most appropriate one. A phone might choose 9V/3A for 27W fast charging, while a laptop would request the full 20V/3.25A for 65W.

The device—not the charger—controls the final power level. A 100W charger connected to a phone that only accepts 27W will deliver exactly 27W, no more. This is why USB PD is inherently safe.

USB PD Versions and Their Capabilities

USB PD has evolved through several revisions, each expanding capabilities:

USB PD 2.0

The first widely adopted version established core functionality:

Fixed voltage profiles: 5V, 9V, 15V, 20V
Maximum 100W (20V at 5A)
Required USB-C for 3A+ currents

USB PD 2.0 enabled practical laptop charging and fast charging for phones. Most chargers from 2018-2020 implemented this version.

USB PD 3.0

Added significant enhancements:

Programmable Power Supply (PPS): Allows voltage adjustment in 20mV steps
Fast Role Swap: Seamless switching when power sources change
Extended message support: Better error handling and status reporting

PPS proved particularly valuable for phone manufacturers, enabling more efficient, cooler fast charging by precisely matching voltage to battery needs.

USB PD 3.1 (Extended Power Range)

The latest revision dramatically increases power capabilities:

Up to 240W: Uses new 28V, 36V, and 48V profiles
Maintains backwards compatibility: Still supports all previous profiles
Enables laptop replacement: Gaming laptops can now charge via USB-C

USB PD 3.1 requires cables rated for Extended Power Range (EPR), marked accordingly. Standard cables safely fall back to 100W maximum.

Understanding Voltage and Current Relationships

Power (watts) equals voltage multiplied by current: P = V × I. This relationship explains why USB PD uses multiple voltage levels:

Why Higher Voltages Matter

Cables have resistance that causes power loss, calculated as I²R. Higher current means significantly higher losses. By using higher voltage with lower current, USB PD minimises cable losses while delivering the same total power.

Example: Delivering 45W

At 5V would require 9A (impractical for thin cables)
At 15V requires only 3A (manageable for standard cables)

This is why laptop charging uses 20V—the high wattage would be impractical at lower voltages.

PPS: The Precision Approach

Programmable Power Supply takes this further by allowing voltage fine-tuning. Rather than stepping between fixed voltages, PPS allows adjustment in 20mV increments.

Benefits include:

Charger can precisely match battery voltage needs
Reduces heat generation in the device
Enables faster charging as battery temperature stays lower
More efficient overall power transfer

PPS Tip: Samsung's Super Fast Charging 2.0 and similar technologies require PPS support. If your phone supports these features, ensure your charger explicitly mentions PPS compatibility.

Practical Implications for Consumers

Charger Selection Guidelines

When choosing a USB PD charger:

Check the full PDO list: Ensure the charger supports voltage levels your devices need
PPS for Samsung/Google phones: If you have these phones, PPS support enables fastest charging
Wattage headroom: A 65W charger can deliver 45W to one device while still having capacity for other ports
Cable requirements: Above 60W, ensure cables are rated for higher currents

Troubleshooting Slow Charging

If USB PD charging seems slower than expected:

1. Verify cable quality: Low-quality cables may not support full USB PD signaling

2. Check charger specifications: Not all USB-C chargers support USB PD

3. Confirm device support: Older devices may not support USB PD at all

4. Heat management: Devices throttle charging when hot

5. Background activity: Some devices charge slower during heavy use

Multi-Device Charging Considerations

When using multi-port chargers, understand power sharing:

Total wattage is typically divided between active ports
Most chargers reduce per-port power when multiple devices connect
Some premium chargers maintain full power on primary port
Check product specifications for exact power sharing behaviour

The Future of USB Power Delivery

USB PD continues evolving to meet growing power demands:

Extended Power Range Adoption

As 240W cables become mainstream, expect laptops that currently require proprietary chargers to transition to universal USB-C. This standardisation benefits consumers through interchangeability and competition-driven pricing.

Integration with Other Standards

USB PD is incorporating support for technologies like Intel Thunderbolt, enabling single-cable docking solutions that provide power, data, and display connections simultaneously.

Improved Communication

Future revisions may include enhanced status reporting, allowing devices to display more detailed charging information and predict completion times more accurately.

For Australian consumers, USB PD represents the future of device charging. Understanding its principles empowers you to make informed purchasing decisions and get the most from your charging equipment.

Written by Michael Reynolds

Michael Reynolds is a lead editor at USB-C Charger AU with years of experience in consumer electronics and charging technology.