In case you're still wondering about power conversion, here is a good site about Serbia's voltage. I was pleasantly surprised to learn that I won't need a power converter for my macbook or iphone (the only electronic devices I'm bringing). Macbooks and iphones and most other modern phones and computers have a power converter built in. If you're wondering about your device, look at its charger or its specs and see if it says it can operate in 220-240 volts. (Standard US voltage is 110-120, but in Europe it's 220-240.)
If you're bringing a hair-dryer, though, you will need a power converter, unless you have a fancy one with a switch that changes its voltage to 220-240.
BUT - no matter what, you will need a plug adapter because European outlets are a different shape than ours. I have one like this from a previous trip that has all the different configurations built in. You can also buy sets of the different plugs.
There are also kits you can buy that have the power converter and plug adapter all together.