I think the most useful electrical equipment are:
CD player: because almost everybody use CD format for listen to music, and the CD player let us listening to it wherever we are.
Remote control: because it help us to change TV Channels non-stop while we are lying on the sofa.
Microwave oven: Because current society has became adept to use it for many ends like cooking or warming food.
Mobile phone: We've became adept to phone everyone and everywhere just for little things.
Fax machine: I used to use it a lot on my job to send messages or any notes,