Thank you for the replies, guys.
I can't say those were the answers I was hoping for, but they shed some light on my next steps.
I have a linear (the hefty type!) transformer that is 120V to 15V, but that thing weights almost a ton. Anything built using it will hardly be something portable. It will do the jobs and they schematics are fairly simple and I've understood most of its concepts.
I believe SMPS are a lot lighter and more efficient than linear PS, right? I guess I'll be searching they web for schematics for such projects (simple, small SMPS) so I have something to start with, but if there is one you guys can recommend, it will be very welcome.
About the oscilloscope, I don't have one and I probably won't have one for a few months. They are simply too expensive in Brazil. I plan on getting this one in a few months.
thanks!