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No, Delegated Steem Power are Steem Power that does not belong to you whose effect are applied to you. So while you do vote with the vesting of the extra Steem Power, only the the original owner of the Steem Power can do anything to it. Either add more delegated SP or withdraw them back to their own account.

No! If you look closely at your wallet, Delegated Steem Power is separated from your Natural Steem Power with a parenthesis. What these means is that while you are enjoying the benefits of the added Steem Power (increase on upvote worth and bandwidth increase), it still is technically "not yours", thus it's not counted when power down.

No.Power down is only youre steempower without delegated steem