Power Gain vs. Power Flood

What is the difference between these two buffs? I do not have a lot of champions with either of these abilities, so I was wondering what the difference was. Please help.
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Power flood is usually set at the same rate everytime.
Power gain can be different in many ways, like a node says power gain is increased by 100% so every hit would give 100% more power, or like hyperion's power gain buff.
Power flood is pretty much a buff that gives power like hyperion's power gain does, it never changes really(idk if in another quest the power given is reduced or raised through out all the content, doubt it.)
Power flood is a buff with continous power gain over x seconds or for the whole fight if it's set that way.
Power gain is usually associated with getting hit or hitting the opponent, gaining more power for every hit. Or in other cases like hyperion and his power gain buff.(which should be called power flood now that I think about it.)
Hopefully my confusing comment helped.
maybe trucos?