When I measure a 9V DC wall adapter power supply with a multimeter it shows 11.8V. When connected to my board this voltage lowers to 10V. Is this normal? Should I be afraid of toasting my 1117CD-5.0 supplied board when using this adapter?
Edit: This regulator accepts up to 12V inputs. So that will be no problem. A second "9V" adapter yields 15V to the multimeter. Will this one burn my circuit?
Answer
Yes, this can be normal. There are two kinds of wall-warts -- regulated and unregulated (the latter are usually cheaper).
You have two of the unregulated ones. These provide their rated voltage (e.g. 9v) under the load specified on their label, but the no-load voltage can be much higher as you have discovered. It probably won't hurt to use the one outputting 15v, since under the load of the board it will be closer to its rated voltage. But frankly, I wouldn't chance it. Use the other one instead.
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