You can't really go wrong with these. It's just a transformer in a box. 300 VA models are easy enough to find. The "Super" brand seem well made. As previous posters mention, these can be bought on Apliu Street. I bought mine at Hung Kwong Shopping Arcade on Tung Choi Street. 150 VA for $135 - housed in metal enclosure with fuse and overlaod protection (some kind of relay). I bought another for travel. 100 VA (step up/step down) in a plastic enclosure for $80.
Don't connect motors (hairdryers, vacuum cleaners )to these things unless you know what you are doing.