Engineer Compares 140 W and 240 W GaN Chargers, Then Starts Building His Own PD Module

A hobbyist engineer has published a write-up on Habr about gallium nitride chargers. It centers on two adapters: a proven 140 W GaN unit that the author took apart and repaired in a previous article, and a 240 W GaN unit from a marketplace. The second claims nearly twice the power at roughly 15 times lower price. The comparison came out of a work task: for one of their projects, the author needed to develop a power module with Power Delivery. The announcement of the publication does not include measurement results, so what follows is the technical context you need to make sense of the numbers on the labels.

Where 140 and 240 W come from

Before PD 3.1, the USB Power Delivery specification topped out at 100 W: 20 V at 5 A. Revision 3.1 added the Extended Power Range (EPR) mode with three new fixed voltages. Power is voltage multiplied by current.

• 28 V × 5 A = 140 W
• 36 V × 5 A = 180 W
• 48 V × 5 A = 240 W
• PD 3.0 limit without EPR: 100 W (20 V × 5 A)
• Price difference between the two adapters, per the announcement: about 15 times

There is a limitation that people often forget. A current of 5 A is allowed only through a cable with an e-marker chip, and EPR mode switches on only after a separate negotiation between the source, the cable and the device being charged. A 240 W adapter without a correct implementation of this protocol remains an ordinary adapter rated at 100 W or less.

Why a 15x price gap raises questions

GaN transistors can switch at higher frequencies, which allows smaller transformers and chokes. That is the main reason compact adapters at 140 W and above became possible at all. But even at 95% efficiency, a 240 W adapter dissipates about 12 W of heat inside a small enclosure. A good adapter saves on size, not on component quality, and is priced accordingly.

For very cheap devices, the typical weak spots are well known:

• the wattage on the label is the total across all ports, while a single port delivers noticeably less;
• EPR is advertised but not actually supported;
• input and output capacitors are chosen with no margin;
• insulation between the primary and secondary circuits does not meet safety requirements;
• output ripple exceeds what a sensitive load can tolerate.

This is a general list of risks, not conclusions about the specific device in the article. The author gives detailed teardown and measurement results in the original.

What changes when you design your own PD module

When you design the adapter yourself, you have to account for things a buyer usually never sees. The controller must handle negotiation correctly, including EPR. Every component on the bus must withstand 48 V with headroom, which makes 63 V capacitors a practical minimum. Another separate problem is current and voltage surges when a cable is hot-plugged under load. This is where the difference shows between a certified design and a copy of a circuit that nobody has validated.

How to test an adapter before plugging in an expensive laptop

A cheap 240 W adapter deserves a multi-step check before you connect any device that costs more than the adapter itself.

1. Take a USB tester with PD support and see which profiles the adapter actually offers. The 48 V profile must be on the list. 2. Use a cable rated for 240 W with an e-marker. An ordinary 60 W cable will not work here. 3. Load the adapter to 70–80% of its claimed power for at least 30–60 minutes and monitor the case temperature. 4. If you have an oscilloscope, check the output ripple under load. 5. Look for USB-IF certification and safety marks, not just the word GaN on the box.

If the adapter fails the first two checks, treat the wattage on the label as a marketing figure, not a technical specification.