All the HAM power supplies I'm familiar with are only adjustable to 15V
out of the box. However, any of the newer switcher supplies are Vmoddable, just like the one in your article to go higher (within limits). 18V should be easily attainable with 90% of the switchers. Just be sure it isn't a
linear power supply
As far as the low end, why would you want to go below 5V, short of turning it off completely ?