Came up in a thread, thought I’d address this in a separate thread to make it more searchable
There is a big box of old wall warts on the north west wall of the lab. Sometimes they need a bit of a load to measure the right voltage. On the back it should say like 18V 800mA that means it will be that voltage at that current. But don’t sweat it if your current isn’t EXACTLY that.
BUT!
Take 2 9v batteries. Hook - of battery A to the + of battery B. THEN the voltage from the - of B to the + of A is 18V and nothing blows up… probably.
Diodes are typically half volt drop. Use a few in series to shave a few volts off. Keep an eye on the current though an LED isn’t going to handle an amp.
Boost converters make a voltage higher, buck converters make a voltage lower.so you can take a 12V wall wart and make 18V or a 24v wall wart and make 18V. I keep adjustable at home in case I need them.
18v wall wart… is an ac/dc switching converter. A search for ac dc converters come up with all sorts of stuff
Every linear regulator is an adjustable, just not under its rated output. So with the right pot you can dial in 18v on a 5v linear regulator (7805 for instance)
There is a circuit called a capacitive dropper. Also you could use a transformer. These drop the 120ac into a lower power that can be rectified and smoothed with a bridge rectifier and caps.