eccentric -> mostly in force there is contribution of passive elements, and less of active elements (cross-bridges). Because of lengthening the "damage", which is more in reality sensing of receptors leads to, generallly, addition of sarcomeres in series. So lengthwise the muscle cell will grow, and in parallel some addition can be done because there is some activity of myosin-actin.

In case of drop set, there is more fatigue, and you keep training with lower intensity or load, but because of higher fatigue, you keep on getting more higher or highest threshold groups. Also there is both eccentric and concentric work done, so more addition of parallel sarcomeres (at least in theory).

With the eccentric training the question remains how soon or how many highest threshold groups are involved as the passive elements can contribute a lot towards the force production. It might be that less high(er/est) threshold groups are activated. Eccentric training can be done with overload, as in very heavy weights only eccentric, with less voluntary control. Or with for instance a bit more load which can still be controlled.

Eccentric has more muscle damage related to intensity, because of higher loads, while drop sets have less high loads and more fatigue, so there would be in the first, hypothetical more mechanical damage, and in the second more metabolic damage. However, the question is open if muscle damage contributes to HT in the first place.

So drop set with controlled eccentric movement in the exercise might be better for overall hypertrophy as you train both eccentric and concentric.

What kind of adaptation would you expect when supersetting a dropset with with a an eccentric exersize after? Would this build size with additional strength? Or does it get the muscle more worked causing more hypertrophy, or does it even Do anything because you would see hypertrophy but adding eccentric exercise to a tired muscle wouldn’t recruit additional neuro-muscular action?

drop-set -> more contractile elements will enlarge. Eccentric exercise -> more passive elements will enlarge + some contractile elements.

If you do drop-sets and fatigue the muscle and afterwards perform eccentric exercise you have a chance to even hit the passive elements more, because the muscle is already fatigued much. So even more force will be produced by passive elements. However, it is also dangerous to perform that. So even if you would have more impuls for HT, you still will end up with less HT after recovery. As a muscle need to be recovered also.

Additional strength is hard to connect to just hypertrophy. Eccentric exercise will form mostly eccentric strength because less contractile elements are involved.

So doing the two exercise could be beneficial if you know exactly how to recover from it. Otherwise it would, or could be less effective.

A tired muscle will not so much recruit additional neuro-muscular action in all situations but can lower the threshold for high(er,est) motor units to be involved. So these can be involved quicker with fatigue and eccentric, but as said will mostly use the passive elements.

Only if the drop-set itself would not be optimal for certain reasons the eccentric exercise after will be really effective strength wise.

Eccentric will however add sarcomeres in length/series so that might be an extra to the drop-sets where you would not overload or hit the eccentric phase optimal.

So especially the passive elements and in series sarcomere adding can be expected with eccentric training.