A lot of the old wall warts are "Type 2", which means transformer, rectifier, reservoir capacitor -- no regulation there at all. With light or no load, the out

A lot of the old wall warts are "Type 2", which means transformer, rectifier, reservoir capacitor -- no regulation there at all. With light or no load, the output voltage can soar (such as, 18v DC no-load from a nominal 12v DC @ 300 mA wart). The switchers are regulated, so you get what it says on the tin.