A variable power supply is a basic piece of test equipment.
I am a nomad, so a portable solution was necessary.
By setting a cheap step-up dc-dc converter to accept a range of inputs and output 32 volts, then connecting it to a variable step-down converter, we get a power supply that accepts a wide range of DC inputs, and outputs anything we want between about 2-32V. It's a simple solution and I'm sure thousands of people have done it, but I'll document it anyway.
These DC-DC converters are available from dx.com, bangood, and electronics markets in various developing countries.
In my case, the converters are from Ban Mo in Thailand, the wires and LiPo (not shown) from Nhat Tao in Viet Nam, and the case and dials from Ahikabara, Tokyo.
A display could be added but seemed unnecessary as I already have a portable multimeter and oscilloscope that can do that.