What I wanted to add is that just because a brick or wall wart says it puts out 12v doesn't mean it puts out exactly 12v. I have boxes of them that I'll pull from for small projects like testing LEDs and I have to test each to find out what it really puts out. Often they are well above the stated output and not by just a volt or two.
Yes often true, IF these are transformer and diode rectifier based, designed for a specific application and load, a no load voltage test will read high
rather switching style power supplies which will read near correct open circuit no load or load