Ok, so I have a Peavey Rage 158, and a 75 watt inverter for my Jeep. As far as I can tell, the input wattage for my amp is 40 w, would I have any trouble running my amp through the 12v plug then?
"Kill one man, you're a MURDERER. Kill many, and you're a CONQUERER. Kill them all and you're a GOD."
Your outlet in your house can put out like 20,000 watts or something like that, if the wattage draw is less than the max wattage of your source then your fine, if it exceeds your source, then you got problems.

I would think that you would drain your battery pretty fast that way too, car batteries can put out like 400 amps at god knows how many watts, problem is, it's a limited source.