I have an SS1500 myself. Sounds to me like it's battery time.
You have a couple suspect issues. One, if you attempt to use the RT lift system with a low battery even if you are shore powered, the draw from the RT Lift system will overload the converter and possibly fry it. You MUST have a charged battery in the circuit, same applies to the jacks if, they are electric. A charged battery must be in the circuit.
Secondly, you have a 35 amp WFCO converter and it's a cheapo converter. I suggest replacing the guts with a PD 4000 series upgrade. I suspect you have already fried the WFCO by running the lift sysrem on straight shore power as the current has to go through the WFCO to actuate the lift motors.
Thirdly, You need to replace the battery and you need to monitor the water in it. The SS units come with one Group 27 battery. My personal opinion is, it's marginally enough. I scrapped the plastic battery box and built a double battery box and I tun a pair of 27's in parallel. You really need 2 batteries, not one.
In order of revelance:
Get a new battery or batteries
Upgrade the WFCO with a PD 4000 series drop in upgrade.
Maintain your battery level, check the electrolyte levels regularly and top off with distilled water.
You can operate the lift system manually with a cordless drill but it's a real PITA and the RT lift system is stone reliable. Your converter isn't.
Many threads on there about the WFCO's reluctance to go into bulk charge mode. Much easier to upgrade to a real converter.
Hope that helps.