Power inverters that convert 12VDC to 110-120VAC usually produce alot of noise, the AC output is either a square-wave or sawtooth-wave output instead of the nice smooth sine-wave output that audio gear needs. The noise filtering in an AC pwr supply was designed to filter the sine-wave output but it doesn't handle a square wave or sawtooth wave output very well. There are higher-end DC-AC converters that produce a much cleaner AC output but the price of them rises very rapidly as compared to the more common and less expensive DC-AC 12V converters. What's really sad is that the power supply in a home DVD unit takes the 120AC and converts it (in many cases) to 12 or 24VDC and then that is further regulated down to a 5VDC B+ supply line for the digital components.