I would dare say that 99% of consumer electronics made within the past 5 years support both 110v and 220v power sources, so it's really just a matter of the shape of the plug. Two prong US plugs work well all over China so you really only need an adapter for 3-prong US plugs and those big UK plugs (which are standard in HK). I usually use my computer to charge all of my phones, routers, and other random gadgets. For less than y20, you can buy a USB cable that supports almost every small device under the sun (of course, your phone presumably came with its own USB cable; I just like the convenience of only having to pack a single wire in my computer bag).