Im eMac Service Manual Seite 11f findest Du die Lösung:
The display/analog assembly contains a non-switching power supply which is preset at a 220V configuration.The voltage selection needs to be manually set by the way of a voltage jumper. This means if you are operating the computer in a 110V environment, you will have to install the voltage jumper.
Dann kommt eine Tabelle der Jumperstellungen und Bilder, wo die Jumper zu fnden sind. Das Manual gibt es hier: ftp://grijan.cjb.net:21000/macintosh/Manuals/emac.pdf