Regulable power supply

Are you wondering what this post has to do with a Raspberry Pi? I'd say a lot, since one of the magic things of working with a RPi is the ability to connect to thousands of circuits via its GPIO. On doing so, you may need 3.3 volts, or just 5 as a USB cable, why not 12 for DC motors?, etc.
Some time ago I bought a LM2596 DC-DC Voltage Regulator Adjustable Step Down Power Supply Module With Display in order to build my first own regulable power supply. It appeared to be easier (and even cheaper) than going with any of the hundreds of DIY circuits available on the Internet.
But then I realized the main problem here was the voltage transformer and even more, I'd need a diode bridge to get DC since the LM2596 board is DC to DC regulator.
Lucky me, issue 4 March 2018 of HackSpace magazine contained an article about building a regulable power supply using the LM2596 based board and... a laptop power supply. It turned out most of laptop power supplies are about 19.5 volts and 3.3 amperes which is more than convenient for lots of applications.
Thank you Ricardo Caja Calleja for showing me how an old laptop power supply could be the key component in my project, and with some additional components (potentiometer, plastic enclosure, banana female receptacles) my regulable power supply is now the latest addition to my toolbox at the lab.