Well, there are lots of PSUs called "Off-line" SMPS (switch-mode power supplies), meaning their source of power is the AC mains, i.e. "line" voltage. There are tons of good dc-to-dc converter Application Notes at the websites of the SMPS controller-IC manufacturers, such as ti.com, national.com, linear.com, and others. I think that TI also still has the old Unitrode appnotes on line, too.