) writes:
I have a few old transformers that output 12volts at 300milliamps.
I was wondering if it was all that important to use resistors to get
the current within the stated specs for a pc case fan I wanted to try
to run on it.
I have a fan that states 0.2amps and another that states 0.45amps.
Would it matter much if I used this transformer for either of these
fans as it is now?
Or would it likely ruin either fan?

This is not a repair issue.

Current is something that's available, and something that's used, not
something that is forced. So if you have a power supply that supplies
more current than the load requires, the load merely takes what current
it needs, and leaves the rest.

It is voltage that is forced. Connect something to a voltage supply
that is higher than needed, and you may burn out that something. Connect
soemthing to a voltage supply that is lower than needed, and it likely
won't work because there's not enough voltage.

On the other hand, some of those AC adaptors are marginal. They expect
to work with a certain current load, and thus they can be made cheaper.
If they aren't loaded to the specs, the voltage may be higher than
it says in the specs. Those expect the load to bring the voltage down
to where it should be. WIth those ac adaptors, connecting a lower
current fan may mean the voltage is higher than desired, and that may
be bad for the fan. It depends on how much higher the voltage.

Michael