I've been to mainland China a couple times; the outlets in the hotels I stayed in were the same shape as the US (and if they weren't, they still accommodated US plugs) but don't let that fool you into thinking that your devices will always work.
It's kinda weird, one time I took a camcorder there and had no problems with charging. Didn't need any converters or anything, but then another time I found myself unable to recharge a digital camera, it didn't accept the power or something.
So to be safe, buy a power converter. Do a little bit of research about wattage in China as opposed to wattage in the US and figure out just what you need.
A little side note: I took a PS2 to Taiwan without any power converters and had no problems, it never fried the system or anything. Maybe their system is different from the PRC. But yeah, should look it up. 😛