I like the PowerMax units. Been using them for eight years now.
WFCO's have a bad rep on this forum for failures. Don't have one, so can't confirm.
Where are you seeing no converter voltage? If not right at the converter, the fault might be downstream from there closer to the batteries.
That 8875 deck mount does have a couple of fuses on the output end that you can check. That model also had a jack for a remote voltage stage switch. If you have been using that, try the converter without the remote in the jack. Should do 13.6v only, but that might be all you need.
Make sure it has 120v input to the receptacle it is plugged into. Plug something else in there to see if it works. If not, is that receptacle on a GFCI circuit? Outside receptacle wet in the rain popped the GFCI? Or the circuit breaker for that receptacle on the AC panel? Is the converter the only 120v thing that doesn't work?