In this post, I’ll show a 9V battery portable power supply I made quite a few years ago by originally following this tutorial.
This particular power supply uses a voltage regulator(LM317) to drop down the voltage and dissipate the energy as heat. This means it becomes inefficient at higher currents. So it is most useful to power things that don’t require a lot of power.
But the upside of using a voltage regulator instead of an SMPS(switch mode power supply) is that it has no switching noise. And because it’s powered by a battery it doesn’t carry through any noise from the mains which makes it great for powering more sensitive circuits.
Note: You might consider using an LDO(low drop out) regulator or the highest output voltage will be 1-2 volts lower than the input voltage.