I have two fans that I have mounted in my new equipment cabinet. The fans are run in parallel and will be plugged into a 12V transformer from one of the many that I have left over from various discarded electronic items. So...my question is, does it matter how many amps the transformer puts out and if so what do I need to be cognizant of. I obvioulsy don't want to burn out the fans, but more importantly don't want to cause a fire. Since the fans are 0.1 Amps each what is the total amp load of them run in parallel? Is it .2A? Then, if I have a 12V transformer with a 300MA/.3A output, is that OK to use...(how much higher or lower is it safe to go?).

Lastly...I have the fans built in to the back of my cabinet, on on each side of the hot AVR. They are currently wired to have one pulling air and the other blowing it out....is this more effective than having them both blowing out? I did have to cut a 12 x 6 hole in the back for the wires to protrude from so it is not air tight and there are other wire holes that were already there...your help is GREATLY appreciated.
Thanks!!

As for the fans, yes. In parallel, 12V .2A. Keep in mind you're dealing with very low current fans. Guessing these are radio shack like box fans. With a 12V 300mA transformer (wall wart/adapter I'm guessing?), you'll be fine. If you're really concerned, put a in-line 250mA slow-blow fuse or 300 mA fast fuse just after the positive wire of the transformer. That will blow if say a fan shorts out and tries to overheat the transformer.

As for the fans in the cabinet. It really depends. If it is a closed cabinet or if it has a door that is almost always closed, your current in/out approach is probably best. If it has an open front or sides, and there is room for air to squeeze from the front of the cabinet to the fans, I'd have both fans blowing out. That will force the air to move through the entire cabinet / front to back.

To be clear:

Electrical loads (such as your fans) DRAW current.

Electrical supplies (such as your 'wall wart' power supply) SUPPLY current.

The ratings on each device are maximums, what the fans could draw (up to .2a), and what the transformer can supply (up to .3a).

HOWEVER (and this is where people get confused) - a power supply will only supply what it is asked to by the load draw. Therefore as long as your supply current exceeds your load current, you are fine. In this case your supply is adequate.

A 500 amp supply would also be adquate, and just as safe. Power supplies do not "push" more current just because they are larger, provided it is the correct voltage.

I am using two laptop cooling pads turned upside down to pull the heat from the components and blow it to the back of the cabinet which is vented. I'm powering them with a wall adapter (6 volt) and they are always on. I'd like to build a simple & cheap thermistor circuit (that I can mount to each cooling pad) so that the fans only turn on when the temperature increases. Any ideas?

While yes it is true that a power supply will only supply the current that it is rated, if a load is "asking for more", most cheap wall warts or older power supplies will try to give it, fail, and overheat. A modern switching power supply is likely smart enough to shut down but an older low end supply will simply overheat. Unlikely to cause a fire at this current level but it will clearly overheat and burn components. A fuse is always safe.

As for the thermo switch. If you like to tinker it's worth it but IMO, let it run 24/7 or put it on a switched outlet from the amplifier or overpriced/rated Monster or Panamax system that switches loads. Unless you're turning box fans on and off, it's not worth it IMO.

While yes it is true that a power supply will only supply the current that it is rated, if a load is "asking for more", most cheap wall warts or older power supplies will try to give it, fail, and overheat. A modern switching power supply is likely smart enough to shut down but an older low end supply will simply overheat. Unlikely to cause a fire at this current level but it will clearly overheat and burn components. A fuse is always safe.

As for the thermo switch. If you like to tinker it's worth it but IMO, let it run 24/7 or put it on a switched outlet from the amplifier or overpriced/rated Monster or Panamax system that switches loads. Unless you're turning box fans on and off, it's not worth it IMO.