USB chargers are set to get a major upgrade, thanks to the newly-released USB Type-C 2.1 specification revision, along with a revision of the USB Power Delivery specification published by the USB Implementers Forum. Cables and devices that support the new specification will be able to charge at up to 240W, instead of the current 100W maximum.
This will be enabled through a new Extended Power Range mode, which only turns on when it's certified that both ends support higher voltages. Devices will have to support voltages up to 48V and 5A current to be compatible with the standard.
For your average phone, it's very unlikely that you'll need that kind of power delivery - or that it will be possible to achieve given the thermal constraints, for that matter - but this is potentially big news for laptops. While most ultrabooks and thin-and-light laptops can be powered by USB cables right now, there are some gaming laptops that often require large power bricks and proprietary connectors because they need well over 100W of power to charge faster than the battery drains. Support for 240W charging via USB Type-C could help bring the USB connectors to more devices and make it so you don't need different connectors for every kind of device.
Cables that support the new specification will continue to work with devices that use older versions of it, so a 240W charger can be used with any device that supports it. The USB-IF says that devices supporting USB Type-C 2.1 will have to be electronically marked to ensure you don't break anything when trying to use a high-voltage charger.