The similarities between dynamo and generator are : 

• Both depend on principle of electromagnetic induction.
• Dynamo and generator both are AC source 

Dynamos and Generators convert mechanical rotation into electric power. Dynamo - a device that makes direct current electric power using electromagnetism. It is also known as a generator, however the term generator normally refers to an "alternator" which creates alternating current power.While an electric motor converts electricity into mechanical work, a generator converts mechanical work into electricity.Electric generator, also called dynamo, any machine that converts mechanical energy to electricity for transmission and distribution over power lines to domestic, commercial, and industrial customers. Generators also produce the electrical power required for automobiles, aircraft, ships, and trains.Direct current motors and generators are constructed very similarly. They function almost oppositely at first because a generator creates voltage when conductors cut across the lines of force in a magnetic field, while motors result in torque-- a turning effort of mechanical rotation.

A dynamo is an electrical generator that creates direct current using a commutator. ... It is basically a DC generator, i.e. an electrical machine which converts mechanical power into direct current electrical power. All motors are generators. The emf in a generator increases its efficiency, but an emf in a motor contributes to energy waste and inefficiency in its performance. A back emf is a resistance to change in a magnetic field.