I was looking into building a smps for a car amplifier and had an idea that I could build a 12v amp with a step up output transformer. Any thoughs about how well this would work? Wouldn't I lose less power across the transformer than with the smps?
The transformer would be massive, and sound like crap. An SMPS transformer is small and efficient because it is high frequency. With the right design an SMPS can be up to 80% efficient - you'll not get anywhere near that with an output transformer.