A converter changes one voltage to another. A converter doesn’t change power levels. If you put 100 watts into a converter, 100 watts come out the other end.
A step up converter allows a device that requires a high voltage power supply to operate from a lower voltage source. The converter takes in the low voltage at a high current and puts out the high voltage at a low current. A step-down converter allows a device that requires a low voltage power supply to operate from a high voltage. The converter takes in the high voltage at a low current and puts out a low voltage at a high current. A step up converter is one whose secondary voltage is greater than its primary voltage. This kind of converter steps up the voltage applied to it. A converter converts alternating current (AC) from one voltage to another voltage. It has no moving parts and works on a magnetic induction principle; it can be designed to step up or step down voltage. So a step up converter increases the voltage and a step down converter decreases the voltage.