hello. i bought a speaker to my macbook. but first i have to turn it on. in the country i reside we use 220v, but this speaker is 110v. the power of my equipment is 135w. so all i have to do is to buy an adapter 110v-220v with more than 135w power?
Let's say you bought this speaker, and it comes with a little transformer that transforms 115Volt to 9Volt or whatever the speaker needs. In that case, do _not_ plug in that transformer under any circumstances, but buy a 230Volt to 9Volt transformer instead. Most likely the old transformer has printed either Watts or Amperes on it, so buy one with the same or higher rating.
If your speakers come with a cable that is supposed to be plugged into a 115 Volt wall plug, then I suggest you buy new speakers. You can buy 230 Volt to 115 Volt transformers, but new speakers will be cheaper, look better, and be safer.