So what kind of electric transformer or adapter do Denmark travelers need for the 230 volts coming out of the outlets?
If you bring small appliances, be careful. The shape adapter may not be enough. While basically all personal electronics in recent years will accept both voltages, some older, smaller appliances don't work with the hefty 220v in Europe. Check if the label near the appliance's power cord shows 100-240v and 50-60 Hz. If it does not, you will need a "step-down transformer" (also called a converter).
The converter will reduce the 220 volts from the outlet to provide 110 volts for the appliance. These converters cost a little more than simple shape adapters. Compare prices of converters here.
Heads up: Don't bring any type of hair dryer to Denmark - they are awfully hard to match up with a suitable converter due to astronomical power consumption. Rather check if your accommodation in Denmark has one in the room, or just buy a cheap one locally.