Capacitor across DC input of inverter ???

I saw a picture of an inverter for sale on e-bay. There was a large capacitor installed that was wired across the plu and minus DC inputs. Has anyone ever done this and if so WHY? Is the cap acting as a stiffing capacitor like the ones used on 400 watt and larger sound systems in cars. Is it suppose to help filter charger ripple? I cant fugure out why someone would install a large cap on the DC inputs of an inverter, the invert was a Trace SW5548. I am hoping to learn something. If it is to act as a stiffing capacitor, it would have to be at least 1 farad or 2 farads in size if it were to be able to do much of any help as a stiffener. The battery bank for an SW5548 would be hugh in size and should be able to do ten times better job itself than the 2 farad stiffener could do. The only thing I can figure is it might be used to help filter out ripple from a battery charger. Surges and spikes that might appear on the DC side would be better filter out using an iron core donut. Can anyone help shed light on this subject? It is helps in some way, then I may want to start installing them on my systems.

captarcandspark