The mains power inlet?
Like any amp, the hot and neutral would be the black and white wires, the third prong being ground, and that connects to chassis.
The little blue discs look to me like varistors rather than caps. Transient suppressors. Looks like one between hot and neutral, and one between hot and ground. If they added a cap, the rectangular thing, I'd expect it across hot and neutral as well.
Is your connector broken? It looks like the spring tabs are broken off. A new snap-in connector is readily available, they don;t cost much at all.