Did the Greeks ever adopt foreign equipment ..

[MeinPanzer]

Greeks colonized Fars before 480BC? Or Gaul, for that matter? And no, Massalia was just a coty on the coast, Celts inhabited massive territories.

Anyways, that is rather beside the point - the point is I don't see why we nearly assume that foreigners using gear similar to the Greeks' means they copied them.

The T&Y cuirass appears among the Persians to my knowledge only after the 5th c. BC, and among the Celts it appears after Greek colonization begins in the Rhone delta. We could add to this list the Scythians, too, for whom there is clear evidence of using the T&Y cuirass after Greeks first appear in the northern Black Sea. When you take into account the independent development of armour throughout the Old World in its varied forms at different times, it becomes clear that such similar equipment almost certainly did not appear by chance.

Say, the tube and yoke armor. It was ubiquitous among Celts, until mail came along. Should we assume the most numerous people in Europe, renowned craftsmen, adopted Greek equipment on such a scale after encountering a few Greeks?

We don't know that it was ubiquitous - we only possess a few scattered representations of it in Celtic art or other evidence of its use outside of the Rhone delta. Also, this isn't "just a few Greeks"- this was an important region (the French Mediterranean coast) which was widely colonized by the Greeks, who consequently had sustained contact over centuries with the Celts in their hinterland.