I have a box-full of salvaged components which I use for 'hobby' projects. There are several low output 11 and 12v transformers. If I wanted to power a chip amp could I use two?
You can connect them in parallel, but they need to be same size, otherwise one will be loaded more than the other.
Almost. If you have two 2x12Vac transformers with EXACTLY the same design, you can put them in parallel and you have double the current of each transformer. In practice it is prudent to have a rectifier bridge for each transformer. Even if they are not fully identical, you can use them in parallel AFTER individual rectifier bridges. Then, the resulting combined current is (a little) less than the sum of current ratings.