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USB-A has been the go-to port on PCS and chargers since the late 1990s, offering a fixed 5 V supply at up to 500 ma (2.5 W) for USB 2.0 and 900 ma (4.5 W) for USB 3.0/3.1 hosts. Battery Charging (BC 1.2) pushes that to 1.5 A (7.5 W) by shorting data pins, but anything beyond 12 W usually requires proprietary fast-charge handshakes and nonstandard voltages.
USB-C debuted in 2014 with a reversible connector and a native 5 V/3 A (15 W) baseline. The real game-changer is USB Power Delivery (PD), which negotiates higher voltages and currents to deliver up to 100 W (20 V/5 A) under PD 3.0—and with PD 3.1’s Extended Power Range (EPR), up to 240 W (48 V/5 A).
Power Delivery Capabilities
USB-A Charging Limits
- USB 2.0 Default: 5 V @ 0.5 A → 2.5 W
- USB 3.0/3.1 Default: 5 V @ 0.9 A → 4.5 W
- BC 1.2: 5 V @ 1.5 A → 7.5 W
- Proprietary Schemes: Up to ~12 W (2.4 A @ 5 V) on modern “fast-charge” USB-A ports but nonstandard beyond that.
Bottom line: USB-A is adequate for phones and small tablets, but can’t reliably power modern laptops.
USB-C with PD
- Base USB-C: 5 V @ 3 A → 15 W without PD negotiation
- PD 3.0: 5–20 V @ up to 5 A → 100 W total
- PD 3.1 EPR: 48 V @ 5 A → 240 W maximum
PD also supports Programmable Power Supply (PPS) for dynamic voltage steps (20 mv increments), improving charging efficiency and battery lifespan on compatible devices.
Cable Construction: What to Look For
Wire Gauge (AWG) & Voltage Drop
Thicker conductors reduce resistance and heat. Standard USB-C PD cables use:
- 26 AWG power wires for up to 3 A (60 W).
- 24 AWG or 22 AWG for full 5 A (100 W+) delivery, keeping voltage drop below industry caps (VBUS ≤ 0.5 V, GND ≤ 0.25 V).
Longer runs increase drop: under 1 m (3.3 ft), you can often push 100 W on a 5 A cable; beyond that, opt for thicker AWG or active/repeater cables.
E-Marker Chips & Certification
Cables above 60 W must include an e-marker chip to communicate their voltage/current limits to the host and charger, preventing over-draw and ensuring safety. Always choose USB-IF-certified cables with the proper markers.
EU Mandate & Market Trends
As of December 2024, the EU requires all new mobile devices to charge via USB-C, extending to laptops by April 2026. This common-charger rule will simplify life for consumers, reduce e-waste, and standardise specs across industries.
Choosing the Right Cable
For Low-Power Devices
- Phones/Tablets: USB-C to USB-A (5 V/3 A) or USB-C to USB-C (15 W).
- Check AWG: 28 AWG is standard for 2 A; fine for phones.
For Mid to High-Power Devices
- Up to 60 W: A 26 AWG USB-C cable without an e-marker often works.
- Up to 100 W: Must use 5 A-rated cable with e-marker and 24 AWG+ wires.
- Above 100 W: Only PD 3.1 EPR cables certified for 48 V/5 A (22 AWG or thicker).
Practical Tips
- Prioritise Certification: USB-IF certified, e-marked cables from reputable brands.
- Inspect Quality: Braided jackets, solid strain relief, and moulded connectors indicate durability.
- Mind Length: Use the shortest cable that meets your needs to reduce drop and heat.
- Beware of counterfeits: Fake PD cables misreport specs—verify with a PD tester if needed.
- Stay Informed: Keep an eye on evolving USB PD standards and regional mandates.
Why Romtronic?
At Romtronic, we control every step in our factory—from precision-stranded AWG conductors and moulded connectors to in-house e-marker integration and USB-IF/PD compliance testing. Whether you need a simple 15 W phone cable or a rugged 240 W PD 3.1 EPR solution, Romtronic delivers performance, safety, and longevity you can trust. When your devices demand power, count on our expertly engineered cables to exceed expectations.
Apple Liu, Romtronic’s Marketing Manager, specializes in driving Asian market growth. With a degree in International English and eight years of sales experience in the electronic cable and harness industry, she brings deep industry expertise and a global perspective. She is passionate about Romtronic’s leadership in digital engineering and is dedicated to advancing the brand’s presence and innovation.
