Power supply amp rating.

Stupid question, I have an electronic device I use in my office that connects to the serial port of my desktop. The 9vDC 200ma power supply went out and I found another 9v 600ma supply in a drawer. Would the difference hurt the device or would it just allow for more current if needed? Also when I tested the voltage of the larger supply it read 12v even though the lable shows 9v. Is that normal?

The current rating is fine, any higher one will work.

The variation in voltage probably indicates an unregulated supply, it should settle when its connected.

Thank you Dr.EM! That was fast!

Hi.
the voltage of your 200mA supply (assuming its unregulated, which most of them are) will be 9V when 200mA is drawn, so if less is drawn the voltage will be higher. With your 600mA one, the same applies. because you are drawing less than 600mA, the voltage will be higher than 9V. As a rule this doesn't matter, most electronics has a operating voltage range anyway.

Josh.

Just be careful that the device has some overcurrent protection- if the current on the replacement is significantly higher. An extreme example would be to replace the 200 ma suppy with one that could deliver 20 amps. If the device were behaving normally there would be no issue but if some internal fault occurred you could damage or destroy the device or cause a fire. Of some concern is also the wire from the 20 amp supply to the device - if it can't handle the power supply output there could be a problem - in event of a fault (short or other overload).

600 ma isn't a lot of current but that's all relative - it's 3 times the 200 ma requirement. If the voltage is acceptable I'd give it a try myself unless it were some very expensive device. You could add a fuse - maybe 250 ma (1/4 amp).

I don't want to make it more complicated than it is but also didn't want to let the overcurrent issue pass either.