c623cc, I think you mean mA (milliamperes) or Amp.

mAh means milli-Amp
hours as it applies to battery life.
You're talking about a USB wall wart/plug, right?
A minimum would be 1A (1000amps) but really you should try to get a 5v/1.5A (1500mA). A 5v/2A (2000mA) is even better (then it can be used with passthroughs). Some of the USB hubs work great for this too. BestBuy and RadioShack usually have them and the wall warts.
This one will run a charger (but not a passthrough):
AC to USB Charger Adapter
This one will run a charger or a passthrough and is 2Amps:
2 amp AC to USB Adapter, ideal for Passthroughs