Most electrical appliances nowdays who use a transformer to either run directly or charge a battery do work on a dual input of 110/220 volts.  You can check each one, and at the transformer read out the input voltage, if it says 110/220 volts you will not need a transformer/rectifier.  If it says only 110 volts then you will need one.

And look at the male prongs on the plug-in end, if two of them parallel to each other you will be OK, if three of them (because of the ground prong) then you will need an adapter to match from yours to the outlet on the wall shown below at :

   http://upload.wikimedia.org/wikipedia/commons/7/7a/Australian_dual_switched_
power_point.jpg
  
     

Be aware, in Hong Kong voltage is 200 volts, but still if it says 110/220 volts input voltage you will be OK, you just will need a different adapter for the prongs    Here adapter will cost you from 10 to 15 Rmb