There are about 20 plug socket types being used around the world today, but only one really matters for modern devices: USB-A. And USB is truly a worldwide standard. Practically all the devices I might carry around – phone, tablet, watch, camera — can be powered directly via USB cable. My next laptop will be powered by USB. Even my Philips electric toothbrush can plug into a USB socket.
It’ll be several years until we can expect to see USB-A and USB-C sockets in the same places that we see plug sockets, which means I’ll still have to carry around charger bricks and plug adaptors when I travel abroad, but if you’ve flown on a plane or stayed in a modern(ish) hotel in the last couple of years, you’ll have spotted USB sockets.
This is a wonderful thing, the peace dividend of the smartphone wars. If I was staying in a hotel or friend’s house in practically any country, I could be sure of borrowing a charger cable or adaptor. Just think of all the waste and pointless peripherals avoided. Other dividends include the widespread usage of 4G/LTE and wifi standards, and soon enough we’ll be able to add wireless charging.
I’m curious to see if and when USB-C replaces USB-A as the socket type of choice. There’s a lot to like about USB-C in terms of reversibility (no getting the plug upside-down), increased power output, and size. But given the typical cycles of replacing infrastructure in hotels, airports, cars, planes, etc., I imagine it’ll be another decade before that really happens.
mssv 
It’s not just happenstance, it’s regulation: China mandated all phones use micro or mini USB as their charging standard, appalled as it was with the amount of landfill used by proprietary phone chargers, and Europe followed suit.
I have the new 12″ MacBook with USB-C, the new 29W charger is barely larger than an iPad one (and it can charge the 12″ iPad Pro 40% faster than its own charger).
Unfortunately, USB-C is a new standard and there are a huge number of dodgy cables that can fry your hardware (even Apple had to recall its initial batch of USB-C charging cables), so caveat emptor.