On the subject of European plug adapters and power converters.

You will need either a plug adapter or a power converter to use U.S. electrical equipment in Sweden. A power adapter simply makes your U.S. power plug fit a European power receptacle. A power converter is BOTH a transformer (modifying voltage and/or cycle rate) and provides a U.S.-style receptacle into which you can plug your device.

Here is how to know which you need:

If you have Laptops and other equipment with a transformer on the supply cord:
Check the label on the transformer or electrical device and look for the input voltage.

• If it says something like this: 100-240 VAC, 50-60 Hz, you're in luck because you have a internationalized transformer which can adapt to the difference voltage and cycle rates of European power sources. All you need is a set of plug adapters to match your U.S. plug on your power cord to the style used in Europe. (U.K. = "C", France = "D", Denmark = "D", Sweden = "D"). See attached PDF guide.
  
  
• If your device says: 120 VAC, 60 Hz, you need a power converter, NOT a plug adapter. Most European power is delivered at 220-240 volts AC (VAC) and 50 Hz (cycles per second) versus 120 VAC 60Hz in the U.S. This will play havoc with (and possible damage) your motors and electronics unless you convert the power to the U.S. standard.
  

If you have something (like a razor, hair dryer, etc.) without a transformer, then you need a power adapter.

Both plug adapters and power converters are widely available in major international airports around the world and in local electronics stores. Radio Shack (see link here) has individual power adapters for $7-8 each. The entire set plus power converter should run you $25-40 maximum in the airports. I got mine for $38 (paid in euros) in Frankfurt last year.

Here is a link to an online "wizard" which will ask you a set of questions and help you decide what exactly you need.