It depends on where you is your accommodation. Most hotels in hongkong are using the electrical plug which same as we use in singapore.
However, some economy class hostel are using slightly different plug. My suggestion is you go to any electrical shops in singapore (e.g. in chinatown), tell them you looking for an "international electrical plug". There are a lot of varieties, but just choose the hongkong one (three round pins).
The other way, you could find one in the changi airport shops. No worry.
