The Apple iMac 21.5-inch (Model A1311, 2009–2011) operates on a universal 100-240V AC, 50-60Hz power supply, consuming between 205W and 241W. This means it can be used worldwide without a voltage converter, only requiring a plug adapter for different socket types.

Apple Support
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Key Technical Details:
Voltage: 100-240V AC (Auto-switching)
Frequency: 50Hz to 60Hz, single phase
Power Consumption: 205W (Mid-2011) to 241W (Mid-2010)
Compatible Models: iMac 21.5-inch Late 2009, Mid 2010, and Late 2011
Power Supply Unit (PSU) Part Numbers: Commonly 614-0445 or ADP-200DF