The temperature drop when unplugging the power can be attributed to Intel's SpeedStep technology, which will conserve energy while working on battery by dynamically decreasing/increasing the clock speed.
There is no way to control this from Mac OS X itself, but for your processor you could use the 3rd party software CoolBook. I have no experience with this software though, and I'd be cautious, there really is no good reason to go fiddling with these settings manuals.
I found the problem, so I thought I'd update here in case anyone else has this issue.
I'm running a 13", MBP with OS X 10.6.8. This problem will not present itself for previous versions of OS X but will likely appear in later versions.
A few weeks ago I installed some Adobe CS3 software - particularly the Design Suite, although I had later versions of photoshop and dreamweaver already installed. As part of the CS3 suite, I installed Adobe Version Cue CS3. This software does NOT play nice with OS X.
At first, I tried manually removing it (easier for most uninstalls in my opinion). This was a big mistake. When I deleted the preference files, my CPU began running at over 100% for "CrashReport". This didn't stop until I restored via Time Machine (thank God for Time Machine!)
Secondly, I disabled it, which did lower launchd and others by 5% or so, but did not ultimately result in my machine running cooler, or my battery lasting longer.
Note: my fans would come on full speed even while the computer was idling!
Finally, I ran the complete Adobe uninstaller for CS3 suite which cleaned up my problem completely. Turns out Adobe CS3 is Unsupported for Snow Leopard although quietly. You can barely find any mention of this on adobe.com and the software still seems to install quite fine.
Bottom line - if you have a Snow Leopard Macbook Pro - do NOT install Adobe CS3 software - in particular Version Cue.
Best Answer
Using any teleconferencing software (Zoom, Google Meet, Cisco WebEx) puts a heavy load on the CPU and the GPU processing the video stream. My 2019 MBA's fans ramp up and the Mac gets hot when participating in a Zoom with 10 people.
My iMac at home, with a dedicated GPU and a very fast Core i9 CPU, shakes it off and barely breaks a sweat, even in Zoom calls with many more participants.
Which 2020 MBP are you using? The 13" does not have a dedicated GPU, whilst the 16" has an additional AMD Radeon Pro GPU of various flavours, depending on the build.