As i understand, Warboy also stated that cases 6-10 is possible in OpenXcom. But he don't want talk clear about his position. I see a contradiction in his words.
I see no contradictions. The code of explosion damage was written by me and Warboy didn't deeply investigate this matter as I did (by making dozens of tests, dumping explosion field data, comparing and tuning).
Explosion pattern depends on layout and obstacles. In exact that layout, when neighbour PSs are apart of each other by 6 tiles - 6-10 cases are not possible, and they look exactly as in vanilla. To totally destroy power source you need to apply 120 damage to that tile (50+70). You see these colored damage dumps, I don't have to explain that. If you will make them 7 tiles apart - they will be slighly different (half destroyed PSs). In some circumstances, when damage is less than 50, Elerium item will be destroyed, but PS tile will stay intact. In some UFO layouts that COULD be possible. But not in vanilla.
If some PSs left, then this PSs always filled by elerium in vanilla Xcom. Is it true or not?
No. Elerium is an item, like any other thrown object. It's spawned inside of PS tile. You can destroy PS with plasma, and elerium item will be lying on the ground. Or you can make "weak" explosion enough to destroy elerium, but not enough to destroy PS.
In OXC possible situation, when a PS left, but hasn't elerium. Is it true or not?
As above. The logic is the same.
Calculation of explosion differs between OXC and vanilla Xcom. Is it true or not?
Not quite. Current tile destruction function should work as in vanilla. The only difference here is PROBABLY bigwall divergence point. Because in OXC we introduced more accurate outer wall mechanics. In vanilla they are always treated as square objects, and even explosion can't pass-by diagonally. But it's mostly about the outer side.
In short. In 1.0 milestone it is possible that PS will be intact but won't carry any elerium inside. This is not applied to nightly.
PS. It would really help if SEED string (or something like that) be available as input field in mission generation, just to make battlescapes totally replicable for different people.