I went around and counted that we seem to have around 30 birick and wall-wart DC power supplies plugged in around the house, and many more that are not plugged in which charge or power various devices. More and more of what we buy is getting to be more efficient and lower power, which is good.
But it's time for standardization in DC power and battery charging. In fact, I would like to move to a world where DC devices don't come with a power supply by default, because you are expected to be able to power them at one of the standard voltage/current settings.
One early experiment is on airplanes. I have an adapter that takes the 12v from the airplane, and has many tips which put out different voltages for different laptops. These are expensive right now, but on the right track.
Our other early venture is USB, which provides up to 500ma at 5 volts. Many small devices now use USB for power if that's all they need. There are devices that plug in to USB only for power, they don't use the data lines. Some come with a small cigarette lighter plug that has a USB socket on it for car use. This includes cellular chargers, lights etc.
I think a good goal would be a standardized data+power bus with a small number of standard plugs. One would be very tiny for small devices and only provide minimal USB-level power, a couple of watts. Another would handle mid-level devices, up to a couple of amps. A third would be large and handle heavy duty devices up to say 20 amps, replacing our wall plugs eventually. There might be a 4th for industrial use.
In full form, the data bus would be used for the components to exchange just what power they want and have. Years ago that would have been ridiculous overkill, today such parts are cheap. However, to make it simple there would be a basic passive system -- perhaps as simple as a finely tuned resistor in place of the data components -- to make it easy and cheap to adapt today's components.
A fully smart component would plug into the smart power and get a small "carrier" voltage designed to run the power electronics only. A protocol would establish what power the supply can provide and what the component wants, and then that power would be provided.
To plug older components into smart power sources, a small dongle would be
available hardwired to simply say the device wants the power it wants. This could be as simple as a finely tuned resistor over the data pins, the exact resistence defining the desired voltage and expected current.
Likewise a mass produced cheap component would go on the end of existing fixed-voltage supplies to handle their end of the transaction. This has to be slightly active, to at least listen to the component.
I haven't worked on this enough to figure if you can do all this with 2 wires, but that of course would be great. However, I suspect 3 to 4 wires is more likely.
In addition, an extension of the system would be needed for devices that need multiple voltages. These are almost all in the middle-power need (2 to 20 watts.)
In that case you would define multi-pin plugs and the data protocol would define the voltages on all pins.
Of course, you could ask for AC or DC, and even wall plugs with 120v AC or 220v could speak this protocol. This would actually be a great safety feature, in that the plugs would not provide power until a device was plugged in to ask for it.
The result of all this is that people would buy a DC switching power supply with multiple outputs. Each output would be tunable on the command of the device plugged into it. This would power all the low voltage devices in one place.
Even with such general supplies, it would also make sense to standardize voltages needed. This could allow for even simpler design. If everybody who needed between 3 and 6 volts settled on 5v, one could make block 5v supplies that run many components without having to adjust each output.
This would also be good for homes that run on solar which like to have DC appliances.
Of course, the data bus would not be speed limited. In the end, it would be a replacement for USB 2.0. USB was about data, with a bit of power for very low power devices. This proposal is about data and power together. It could work at low data rates for devices that just need a power negotiation, but it could also provide high data rates so a digital TV could plug in with one plug and get power and TV station digital streams on the same wire. Ideally an IP like P2P bus rather than a master/slave bus as USB is. (See earlier entry on ideal AV system.)