I have the same issue with powerd using up more than one core of CPU on my 2019 16" MacBook Pro on macOS Catalina 10.15.7, and also making my system super slow (despite it "only" consuming a little over one core out of eight). [Edit: The issue is still present on macOS Big Sur 11.1.]
Solutions that did not work:
sudo pkill -HUP powerd (it would immediately restart and resume hogging my CPU)
- closing Activity Monitor
- closing Intel Power Gadget
- unplugging all of my Thunderbolt 3 devices and power adapters
- resetting my SMC
So I opened up Console.app and noticed the following repeatedly:
Process powerd.154 TimedOut UserIsActive "com.apple.powermanagement.wakeschedule" age:00:00:01 id:38654738880 [System: DeclUser kDisp]
This tipped me off to this Reddit post. In it, u/iTim314 notes that he needed to go to System Preferences > Energy Saver > Schedule, and to specify something. I chose the least annoying values possible:
After clicking OK, this immediately fixed my powerd problems. No more powerd warnings in Console.app, powerd was no longer hogging my CPU, and my system immediately became more responsive. If I uncheck both of these values and save again, the problem immediately reappears. And so on. (The Joker: "Ta-dah! It's GONE!")
Unfortunately, this is a workaround, not a true solution, but I'm hopeful this helps others figure out a proper solution or bugfix.
After writing this post, it hit me: This problem seemingly started occurring after I went into the "Energy Saver schedule" dialog two days ago. I took a look, checked (one or) both options, maybe saved my changes (I don't remember), then unchecked the options, and then maybe saved again (if I saved the first time). I've had this MacBook Pro for over a year now (and other MacBook Pros for over a decade) without experiencing this issue, so this probably isn't a coincidence. I'm left wondering if a corrupt .plist is being written for these settings...