In particular, AC current can operate a transformer which can step it up or down easily ... You can’t readily increase a DC voltage unless you convert it into some sort of AC first.

Step-up (Boost) Boost or step-up converters are used to convert a lower DC input voltage to a higher DC output voltage ... Sine Wave This is the best waveform, as it is the shape of an (ideal) AC ...

AC DC converter chips rectify AC input into DC output. They also adjust the voltage level through a regulator and smooth the pulsating DC through a capacitor. This video explains AC to DC conversion.