I changed my WF8955 converter unit out for a Progressive Dynamic PD9260C unit. It fit in the same lower compartment of the WFCO 8900 series Power Distribution Center. You DO NOT have to change the whole chassis out - just the bottom converter/charger unit. The top section containing the AC Circuit breakers and DC fuses does not have to be removed. Contact RANDY at BESTCONVERTERs at the link in the above message. Tell him you want to just replace the converter/charger unit and you want to keep the WF 8900 series Power Distribution unit.
If your WFCO 8900 series Power Distribution unit is getting 120VAC then the WF8955AN Converter/Charger module will always put out 13.6VC. The 10VDC you was reading is coming from your connected battery telling you all of the wiring and in-line fuses between the Battery and converter/charger unit is good. Your converter/charger unit is NOT producing the 13.6VDC when connected to shore power (120VAC).
Roy Ken