If they're the "wall wart" type of plug-in power packs, then you can probably find suitable 220V replacements locally in Hong Kong quite cheaply. Just check for AC/DC output, correct voltage and regulation, current, and connector type/polarity, and you should be fine. Even if the existing power packs output AC which is rectified in the equipment, it's unlikely that the 50/60Hz difference will be of any importance.
If you have a whole bank of equipment or anything with a built-in 120V-only PSU, then it may be easier/cheaper to obtain a 220-to-120V transformer of suitable kVA rating and run some regular NEMA 5-15 outlets from it for your apparatus.
