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Can I use a 12 V DC power supply for an 9V AC gadget? Does it get too hot? Or can it work safely? I tried it already and it seemed to work. Is it safe? The gadget is a telephone.

user59830
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    Maybe, maybe not. It depends on the circuitry in the gadget. – Dampmaskin Mar 22 '18 at 14:10
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    I don't think it's a good idea putting a) more voltage into something b) DC into something which expects AC c) doing both at the same time. – Arsenal Mar 22 '18 at 14:11
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    Being cool on the outside does not prove some little SMD part is not getting burning hot on the inside. It may or may not work. – Tony Stewart EE75 Mar 22 '18 at 14:14
  • @Dave Tweed , that is not a duplicate but rather he was probably told to use a 12Vdc instead of 9Vac and he is wondering why and that is my take on this question. **Not only is it not exact, it is not even close.** – Tony Stewart EE75 Mar 22 '18 at 16:37

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12V dc is about the peak of 9Vac so it should be fine for startup except the voltage regulator may get too hot as the 9Vac under load would drop from 13V to 10Vdc or so depending on load 12Vdc may give a bit more heat loss.

Given 9Vac transformers are kind of obsolete for new design I think a 9Vdc is ideal but 12Vdc may work.

Tony Stewart EE75
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  • But why does it support the "DC" supply? I thought AC and DC are not compatible... – user59830 Mar 22 '18 at 16:31
  • It has no AC motor rather a AC to DC converter with a diode bridge which supports DC. AC supplies were once cheap and diodes failed so it made the wallwort slightly less prone to failure.. But this is old school now with SMPS. – Tony Stewart EE75 Mar 22 '18 at 16:35