Have you checked the output fuses with an ohmmeter or other tester, or just visually? It's sometimes possible for fuses to be blown but appear--at least at first glance--to be okay. Also, are you checking the output voltage directly at the converter, or at the other end of the wires that attach to it? If the latter, it's of course possible that a connection could have failed.
If the converter is getting input power and not producing output power, I'd give PD a call and see what sort of support they can provide. They're usually fairly decent to deal with, from what I've heard, and I'm not sure there are many "better" converters generally available. There are some that are about as good and as well built, but they'd be more of a horizontal move than an upwards one. Most would say that WFCO is worse quality, and PowerMax maybe about equivalent, depending on one's usage etc. If you're plugged in all the time (or essentially all the time), you probably don't need a super special converter, mainly just one that will not continually overcharge the batteries.
