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. 
