Using us iMac in europe

Go to the nearest Apple Store, or Apple Authored Reseller/Service Center and purchase either a new power cable with the correct connector for you European locale, or a plug converter kit. See what the local market suggests for a surge protector too, in case the local power grid deliver is in poor shape. As stated, the iMac power supply is auto-sensing within the voltage delivery limits.

I'm just saying what is typical of all the Mac power supplies I've used. From iMac specs:

Electrical and Operating Requirements

• Line voltage: 100–240V AC
• Frequency: 50Hz to 60Hz, single phase
• Operating temperature: 50° to 95° F (10° to 35° C)
• Relative humidity: 5% to 95% noncondensing
• Operating altitude: tested up to 10,000 feet

The PS should switch between 120 and 240 Volt services. You might need a wall outlet adapter, however.