My son (6 years old) has EZ track running around the ceiling in his bedroom. It started out with the Chattanooga kit, then added another loco and a few cars. For Christmas he got some ore cars, and some flatbeds and a new Loco. Now the train cuts out when he turns it on. After being turned off a while it starts to work again. I was kind of expecting it, thinking that 3 locos would be too much for the power supply that came with the Chattanooga kit. Does this sound right? Can I get a better power supply? I should add that we are relative newbies to model railroading. 

I was really only looking for a snowplow and could only find an old one. Most cars I will buy will be new.

Excellent info. Thank you all. So I don't need to pass on older cars because of their couplers. That's good news.
Thanks again.

Thanks for the helpful info. Another quick question, if a car has horn hook couplers, can they be easily changed out to the newer style?

Hi. I'm new to trains and have set up a Bachmann Chattanooga set for my son. Some of the couplers aren't working anymore and I'd like to buy some replacements. What kind do I need? They have little springs on them. I see short, medium, and long ones listed but don't know what that means or which ones I need. Thanks for any clarification.