did you mean 120vac to 12vdc? I'm going to assume that and then you will not only need a transformer but rectification as well. I think the linear power supplies are still the best but the switching power supplies are catching up quickly. that said Battery/Cap based is better still as long as the battery or Cap system can handle the current demands. something like the below is excellent I've a friend with one in his system and it made a huge difference.
https://www.vinnierossi.com/mini/