Electrical power in Holland and in most of Western Europe runs on cycle of 50hz, and a voltage of 230 Volt, alternating current. In North America, power runs at 60hz/110 Volt.
This means you need to bring a travel converter for such things as contact lens cleaning kits, laptop computers, curling sets and battery chargers. You may need to bring several converters if you anticipate needing to operate these items concurrently.
Converters for up to 2,000 watt equipment are available from luggage- or electronics stores, or — at a higher cost — at the airport. Amazon.com carries a wide range of travel converters.
Most travel converters come with international plugs and adapters, but you may need extra sets for those electronic items that already come with built-in converters (e.g. electronic shavers).
Dual Power Caution
If your laptop, shaver, electronic toothbrush or other electronic item comes with dual-power compatibility, make sure you know how to use the equipment in another country. Some electronics switch automatically. Others need you to manually change a switch.
Consult the manual that came with your equipment. If you no longer have it, look for a voltage switch or dial on the back of the item.