is feeding acceptable or not

[Fal]

absolutely yes, the gems/gold/items should go to the player(s) who have the potential to avenge your defeat. It is, in fact, an important part of the game, and part of your strategy. That is to say, if I can't win, I will certainly not let you win either.

Therefore it is a critical factor that one should always take into consideration before he makes the final kill to his enemy.

However I have seen a case where the player A gave his hundreds of gems to the player B who defeated him, simply because he believes the game is over and no one would be able to defeat play B...a rather cynical move, I'd say.