AC Motors
The AC motor uses power as it comes from your wall outlet. The voltage will depend on the part of the world you live in. These motors last a very long time. When you take an older machine with this type of motor to the shop for maintenance, the sewing machine technician should check the motor brushes for wear.
The downside of these motors is that they do not have very much power at low speed. That means the sewing machine can labor when you need to sew slowly. This can be a problem when sewing over dense fabric or many layers. They can be so weak that when you start to sew, you might have to help by turning the handwheel by hand. Manufacturers have overcome some of this problem with circuitry, but many lower-end sewing machines suffer from this lack of power.