Using multiple power supplies to increase current
1A at 12V is 12W (P = IV). You can step the voltage down to convert this power into more amperage. Specifically, at 3.5V you could get up to 3.4A. Bear in mind that conversions will introduce power losses.

What is the load? You may not even have to limit voltage -- only current.



To answer your question directly, it depends on the type of wall wart. There is a danger when paralleling sources that one of them takes more of the load than the other. This is especially true with regulated or switching supplies, which have feedback systems to regulate their output voltage. It should not be much of an issue when using identical supplies that are a simple transformer, full-bridge and low-pass filter. They won't be perfectly matched, so don't use them to a full 200% of either's power limits. You could put current-sense resistors inline with both to measure their contribution to various loads.