If you have an older iPod USB charger, they do just fine charging up Xbox 360 controllers.
Not the tiny cube charger that comes with an iPhone, but the earlier iPod classic models Third generation and newer. I'd avoid trying an iPad charger though. Too many amps could toast your controllers.
Another easy possibility, if you have the controller USB cord, is to try using the USB port on the older silver Motorola cable boxes or even a Nintendo Wii.
I use the Wii to charge up my PS3 controllers even when the Wii is in use or standby.
I've had a lot of bad luck with Xbox control chargers. Even the official ones from Microsoft sadly.