Caged Sun

As this artifact enters, choose a color.
Creatures you control of the chosen color get +1/+1.
Whenever a land's ability causes you to add one or more mana of the chosen color, add one additional mana of that color.

The Brothers' War Retro Artifacts

As Caged Sun enters the battlefield, choose a color.
Creatures you control of the chosen color get +1/+1.
Whenever a land's ability causes you to add one or more mana of the chosen color, add one additional mana of that color.

Warhammer 40,000 Commander

An ability that triggers from the resolution of an activated mana ability is also a mana ability. This means that if the land's ability that caused you to add mana was an activated mana ability, Caged Sun's triggered ability won't use the stack and can't be responded to.

Commander Anthology Volume II