I’ve recently been doing some detailed research and studying related to the USB Type-C connector and the associated USB Power Delivery (PD) specification. At first, both seemed like such a good idea, but now I am not so sure – especially about the USB PD part.

First, a little background. Like many people, I have a drawer full of AC/DC charger units I no longer use but can’t bear to toss, Figure 1. These units are often derisively called wall warts; many also function as power sources in addition to chargers, to be used with or without batteries in their target unit.

Figure 1 If you have used electronic devices, toys, or smartphones over the past decades, you likely have a drawer or box stuffed with chargers that are no longer needed, but you can’t bear to toss out. Source: Google

These chargers come in a wide range of voltage and current ratings, each specific to the product with which they came. They also have a wide range of frustratingly incompatible coaxial (barrel) connectors (“coaxial” in their physical structure, and unrelated to RF coaxial-cable connectors), and both polarity orientations, Figure 2.

Figure 2 Barrel connectors come in a wide range of inner and outer diameter pairings, presumably to key the connectors to their voltage and current, but actually a source of confusion and waste. Sources: Bid or Buy/South Africa; Same Sky

As a consequence, it is almost impossible to use one AC/DC unit as a replacement for a misplaced or defunct one. While I have resorted to repurposing one with the needed rating but wrong connector by swapping and soldering the correct connector from another unit, the average person can’t do this.

Now, USB-C and USB-PD

Then came smartphone charging and a drive towards more uniformity in USB-based charging, using either the Apple Lightning connector, a USB Type A connector, or others. “Hey,” I thought, “we’re making progress.”

Now, we have the USB Type-C connector, which is mandated by the European Union for all suitable products, including smartphones and, by extension, driving its adoption outside the EU, Figure 3. So it looks like barrel connectors are history, and other USB connectors are falling behind, as USB-C is the way to go. So far, so good.

Figure 3 The USB Type-C connector is poised to dominate due to its capabilities and the EU mandate to be used wherever technically feasible. Source: CNET

Then I started looking into the USB Power Delivery (PD) standard in more detail. It dramatically increases the available voltage, current, and power levels, Figure 4.

Figure 4 The progression of power-delivery capabilities offered by the various USB connectors is impressive. Source: Texas Instruments

USB-PD offers three power-delivery modes:

• Sink: a port, most often a device, that consumes power from V_BUS when attached.
• Source: a port that provides power over V_BUS when attached,
• Dual-role power (DRP): a port that can operate as either a sink or source, and may even alternate between these two states.

It gets messy

This makes it all sound so simple and effective, but USB PD is not like peeling an onion, where every layer you peel back reveals only one other one. Instead, it’s more like nuclear fission, where each action or state change can lead to multiple new ones.

I won’t try to describe all the ins and outs of USB PD. There are many good overviews as well as detailed dives into the standard (see References). To sum it all up: it’s very complicated, starting with a back-and-forth initialization-negotiation dialogue between the two sides of the connection to decide who can do what to whom, Figure 5. An added complication is that USB PD allows for multiple loads to be charged at the same time, each with different requirements.

Figure 5 Once the USB-C connector is connected, the two cable ends begin a sophisticated negotiation about what needs to be done and what can be done. Source: Acroname Inc.

USB PD has many cases, exceptions, state diagrams, timing diagrams, conditional rules…it’s a long list. With all this comes the need for a very smart embedded controller to implement it.

At first, I thought the entire USB-C/PD scenario was the best thing to happen. After all, what could be better than a “universal” charging setup? It promises to handle anything up to the specified maximum, with no action on the part of the user, and no incompatibilities. What’s not to like?

However, the more I looked into USB PD, the more concerned I became. In the attempt to be a solution to just about any charging situation (and let’s ignore the data-connection interface aspect), it tries to do an awful lot. Yet history shows that such overarching objectives, however laudable and well-intentioned, can become a swamp.

That’s where I started to worry. Who can actually grasp the totality and subtleties of USB PD, especially if there’s a problem? Can the controller really be tested to 100% certainty that it properly implements all the rules and cases correctly? Are there corner cases in the real world that will only show up months or years later, with frustrated users as the test subjects?

This isn’t the only example

Whatever happened to the engineering mandate to “keep it simple”? I’ll cite an automotive parallel. Volkswagen recently introduced the 2026 Tiguan SEL R-Line Turbo, which uses a list of engineering approaches to squeeze 268 horsepower and 258 lb-ft of torque out of a modest two-liter, four-cylinder engine.

To do this, they use forced induction turbocharging, where one turbine spins in the engine exhaust, with temperatures around 1,000 degrees, and its momentum is transferred to a paired turbine spinning at speeds above 150,000 rpm to pressurize the air-intake charge. It also employs variable inlet geometry that instantly and precisely meters boost, air charge, and bypass, reducing throttle latency and increasing efficiency. The super-high compression ratio of 10.5:1 relies on higher pressure in the direct fuel-injection system (from 350 to 500 bar) as well as a forged steel fuel rail to carry it.

But why stop there? In a classic example of inevitable follow-on consequences, the higher forces require thicker piston crowns, shortened connecting rods and thicker wrist pins. The need for cooling meant redesigning the combustion chamber itself, and incorporating a new air-to-water heat exchanger. The big turbo-edition comes with oil-cooled pistons and a nitrided crankshaft. Finally, the hydraulic intake cam adjuster replaces two pairs of cam pieces with double actuators and instead substitutes four separate cam pieces with eight adjusters.

 So I have to wonder: what will the reliability and maintenance of this engineered complexity and sophistication be in a mass-produced car?

In some ways, USB PD is the latest iteration of the belief that a universal solution is possible and that “this time, we’ll get it all right.” However, sometimes having just one more-tightly focused objective is a better idea long term, as there are fewer unexpected and unpleasant surprises.

Will I miss the cheap AC/DC charger that does one thing, with its proliferation of power ratings and barrel connectors? No, I won’t. Do I welcome the USB-C and PD standard and implementation? Let’s just say I am cautiously optimistic, as I recognize that it’s a complicated system and not merely an A-to-B power source. My personal jury is out on this question!

What are your thoughts on the complexity and ambitious reach of this power-delivery standard?

Bill Schweber is an EE who has written three textbooks, hundreds of technical articles, opinion columns, and product features.

Related Content

• How does a USB Power Delivery (USB-PD) design work
• Power Tips #130: Migrating from a barrel jack to USB Type-C PD
• USB Type-C protection switch improves safety
• Controllers simplify USB-C dual-role power delivery

References

• USB-C, USB PD, and Coaxial Connectors
• USB Implementers Forum, “USB Power Delivery”
• Embedded, “USB Type-C and power delivery 101 – Power delivery protocol”
• Texas Instruments. “A Primer on USB Type-C and USB Power Delivery Applications and Requirements”
• Simplexity, “Build Better Devices: USB Power Delivery Explained”
• Same Sky (formerly CUI Devices), “How to Select a DC Power Connector”

EU and USB Type-C regulation

• The Verge, “EU proposes mandatory USB-C on all devices, including iPhones”
• NPR, “The European Union Wants A Universal Charger For Cell Phones And Other Devices”
• BBC, “EU rules to force USB-C chargers for all phones”
• Forbes, “EU Proposes Universal Charger—A Blow To Apple”
• Tech Crunch, “Europe will finally legislate for a common charger for mobiles”
• CNET, “USB-C power upgrade to 240W could banish some of your proprietary chargers”
• European Union, “EU common charger rules: Power all your devices with a single charger”

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