Power supply question--so what happens when

I plug my gizmo into the wall using a power supply rated at 9V 500mA, when said gizmo is rated at 9V 250-300 mA?

I hate wall warts.

as long as your voltage and polarity (if it's DC) are correct, the amperage rating shouldn't make a difference, as long as the amp rating of the power supply is more than the device.

and ended up with a power supply that doesn't match anything I own and a missing supply for a gizmo.

What if it's WAY more amps, like 1000 mA instead of 250? Electronics was a l-o-n-g time ago for me.

Voltage is often expressed as "electrical pressure", if I recall correctly. Amperage is the amount of electricity that flows through the circuit.

A way to think about it could be just to think of plugging an appliance into the wall, any old appliance. Now, the appliance is rated for 120v and rated to draw 5 amps. But the circuit breaker is rated at 30 amps. Does it hurt the appliance? Not a bit, it just doesn't blow the breaker.

Now, if you take that 120v appliance and plug it into 240v what happens? Instant smoke!!

I am pretty sure the same applies to your wall wart and gizmo, as long as the voltage and polarity are correct. Hopefully, someone will come along and enlighten us a little further.

Good luck!!

and thanks for the refresher analogy.

Simplest answer is: Nothing. The rating on the wall wart is to tell you how much current the thing can deliver. If the other one was a lower rated power supply, it just means you're using one at half its capability. The voltage will still be the same, and the gizmo won't take any power it doesn't need.
The Professor

if your gizmo is only using 250ma you still have 250ma left, enough to power a second similar device.

to get through the organ solo on "Green-Eyed Lady" do you suppose?

It's a nice solo. Not something one needs to learn. Evoke it. Then just play what's in your head!
The Professor

about all the triplets.

I wonder what "refreshments" fueled that session.

I don't think there's anything to wonder about!! LOL!
The Professor