Well, the 275 watts in input power, that's how PW transformers were rated. For continuous output power, figure on around 75% of that, and that's at full throttle.
If you're only drawing six amps and the breaker is tripping, time to replace the breaker. Many folks use an automotive cartridge type breaker as a replacement, if you use a socket, you can even tinker with the rating of the breaker easily. 
