Q: what is powerd and why is it using so much cpu

Holy cow, that's a very discomforting post!  I hope Apple can grow their backup support into full blown profile support across all a user's devices. 

Here's a simple bash script which will monitor powerd and kill it if it gets out of hand.  Please use this with caution as it's not tested, but it may just do what we need until apple fixes this bug:

Open Terminal.app and type

sudo

and enter your password.  Then copy and  paste this as one line:

while true; do cpu_usage=`ps aux | grep powerd | grep -v grep | awk {'print $3*100'}`; echo "powerd is using $cpu_usage"; if [[ $cpu_usage -ge 3000  ]]; then echo 'killing powerd!!!'; killall powerd; else echo 'no problem'; fi;  echo '# Sleeping for a while'; sleep 60; done

The "3000" value means "30% cpu" so you can adjust this as needed.   "sleep 60" means this runs once per minute, you can adjust that number too.

Not sure if it's a useful data point, but I didn't see it as I was reading the thread. When I discovered my MacBook Pro (Retina 13") in this runaway powerd state, I noticed that there was a terminal window open, too. Never used Clean My Mac, but perhaps that's system software? Again, not clear from reading this thread.

Based on the thread, I did attempt to kill the process from the Activity Monitor. There were two options there, apparently a regular kill and a forced kill, but I tried the regular kill, which may have been a mistake. At that point the Mac appeared to be in some kind of loop of killing and restarting powerd, which also caused powerd to jump all over the Activity Monitor, instead of sitting at the top with all of the CPU cycles...

Next plausible step seemed to be a restart (reboot), which seems to have cleared it up. For now.

Still no idea what the real cause was (though some of the comments in the thread suggest it may recur), though my unnatural paranoia makes me seriously consider the possibility of black-hat hackers. If not the Chinese, there's always the NSA or North Korea, eh? More likely it's just a bug from Apple, but there aren't any pending updates. I was unable to find any log of recent updates or installations, but I haven't been involved in any updates recently... I'd remember at least two or three weeks back if I had. (Only oddity I did find is five purchased but not downloaded apps, but I'm guessing these are just freebies (or free options) from Apple: GarageBand, iMovie, Keynote, Numbers, and Pages.)

Not sure what else to say, but I'm still a bit concerned and of course I'm going to look for later related threads, too.