There is nothing wrong with your AC cord set up. 20 amps is plenty for the converter.
Check the voltage at the battery. If above 12.8V, the converter is fine. If below 12.4 the converter is probably bad or a blown fuse on the input side of the converter.
Report back your battery voltage with the AC connected and when it the AC is disconnected. And let us know if you hear the slide motors attempting to move the slides. Then we can go from there.