It may not seem that the ubiquitous USB cable has anything to do with the power grid. It’s all a matter of current.
The problem is that the universal standard power grid is alternating current [AC], while USB [universal serial bus] cables carry only direct current [DC], in addition to data, for powering devices. In the home, there are a few items that use AC, such as the washing machine, refrigerator, or climate control systems. Since the power grid is already AC, it is very efficient to use appliances that run on AC electricity, but what about the increasing number of DC appliances finding their way into our homes?
“Wait, everything I have plugs into the wall, including my laptop, television, radio, and smartphone,” you might say, which is clear evidence that everything is powered by the AC power grid. Actually, every single one of those devices is DC powered. Some of these might be obvious, such as the multi-USB-ported adapter, which is essentially a block that plugs into a standard outlet and has a few USB ports that you can plug your portable devices into. That block, much like the laptop charger block and smartphone charger block, as well as the hidden ones inside televisions and desktop computers, are AC-DC converters.
Seeing that many things today are actually DC powered, wouldn’t it make more sense to have a DC power grid? USB power has become so ubiquitous that hotels, cars, airport charging stations, and even some new homes are equipped with USB ports. Soon, with a new USB PD [Power Delivery] standard, USB PD cables will be able to carry up to 100W, which will be able to power bigger devices faster. Right now, in order to use your DC devices on an AC grid, the AC-DC converter is needed, but does so quite inefficiently, the side effect being energy wasted as heat. If more devices switch to being powered by DC directly, without the converter, DC power grids could prove to be the far more efficient option.
Image © arz (Own work) [Public domain], via Wikimedia Commons