There is no such thing as Steem Power (SP) in the back end. When you power up, your STEEM is converted to VESTs. When you power down, your VESTs are converted back into STEEM. The conversion rate changes over time, though... so that balance appears to be growing. It's showing you how much STEEM your VESTs are worth.

The reverse stock split shouldn't have any meaningful impact on the value of the STEEM you hold. if you have 23,984.236 STEEM when the reverse split occurs, your balance will become 2,298.423 STEEM. But each STEEM will be worth ten times as much.. so you'll lose 0.006 STEEM of value. Basically a rounding error.