the Supco is a capacitor that give the compressor an extra jolt of electricity to get it started. Usually installed on older units. $15.00. Once the compressor starts it does nothing.
A soft start is an electronic device that slowly ramps up the compressor to bring it up to speed. $300.00. once the compressor has started it does nothing.
Both are used in low voltage conditions.
I'm a Master Electrician and I use a Supco.
2011 Keystone Sprinter 323BHS. Retired Master Electrician. All Motor Homes are RV's. All RV's are not Motor Homes.