It's not hard to imagine how the adapter would work. A USB cable would be sufficient to carry both power and data between a power supply and multiple devices. Each gadget, when connected via USB to the power supply, could transmit its power needs over the cable to a one-size-fits-all power adapter, which would then deliver the correct voltage back through the same cable. Should you find yourself on a trip without your power supply, you wouldn't need to go on a hunt for the correct model, nor would you need to pay fifty dollars for it at a cellphone store. There'd only be one type that worked with all portable gear. Any convenience store could stock them.

There's an obvious greentech angle, too: Smart adapters would be able to turn off the "phantom power" that an unintelligent adapter continues to deliver to a fully-charged phone overnight. When you throw out your phone for a new one, you could keep the adapter rather than adding it to the local landfill and buying a different one for your new model.

Yet consumer electronics manufacturers, usually quick to adopt standards that make their devices interoperable, have balked at switching to a universal power supply. , a startup that makes components for a USB-based single power source system, drew a favorable response from readers when the Standard last summer.

But gadget makers seem to have no compelling financial incentive to adopt Green Plug's technology. It would require them to add Green Plug's chip, or similar hardware and software, into every phone, camera, or music player they build, making them more expensive and more complicated to build.

Another stumbling block for manufacturers: A universal power supply would kill the market for replacement power supplies. Manufacturers sell these at a steep markup price to customers who lose or break the original one that came with the device, and aren't tech-savvy enough to procure a low-cost generic replacement.