Question about low voltage power supplies

I have several wall plug power supplies. The voltage on one says 12v 300ma but on my multimeter im getting 17 volts. Why is it 17v and not 12v?

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tech-king9 years ago
what trialex said is true. this is also why, on the thread of how to convert under car neons to run on house power, i recommended against a wall wart power supply. to correct the problem and ensure an even, continuous 12 volts, you can do one of the following: install a zener diode accros the positive and ground leads to regulate power install a 7812 voltage regulator install a mosfet vcr
Rob K (author)  tech-king9 years ago
I was going to use the power supply to run a 30 LED array. The 7812 voltage regulator might be what I need to help.
tech-king Rob K9 years ago
30 leds in paralelle?? you may draw too many amps for a 7812. consider a zener diode
Rob K (author)  tech-king9 years ago
I think it was around 220-240ma for what im looking at running 33 leds. I was going to run 11 3 LEDs series with 15ohm resistors. LEDs 3.9fv 20ma
tech-king Rob K9 years ago
ohh. in that case, just use the 7812
Rob K (author) 9 years ago
I pluged it into a 12DC fan and checked with the multimeter agin wile it was running around 13v.
trialex9 years ago
Because it's a cheaper model and not regulated. The voltage of non-regulated power supplies typically sag under load - so to ensure they still deliver 12V under load, they produce a bit more when there is no load attached.