POWER up is basically purchases sp.
How to POWERDOWN STEEM POWER
Withdrawing STEEM POWER from your steemit.com account requires that you initiate a process called Power Down that begins to convert your STEEM POWER to STEEM tokens that you can transfer to other users or withdraw and sell. Before starting a Power Down your current STEEM POWER will start to be converted into 104 equal parts and each of them will be available to you in the form of STEEM, now only takes 12 weeks ..
The first portion of STEEM will be available in your wallet after exactly one week, then in another week you will get the second part of the 12 and so on with the process, which 3 months or 12 weeks to complete. At any time you can do Cancel Power Down from your purse just like you started it, but the advice is to stop it once you have received one of the 104 installments.