Looks like demand dropped by 100B kwhs, while supply remains the same. This started about 6 game months ago.
I found this by clicking on the market situation bar (just barely green now), and in the window, I click on the red/green icon right after the number of oversupply. That pulls up a historical graph of supply/demand.
Looking at the world supply/demand graphs, it looks like it's almost every sector taking a nosedive, but some sectors are already recovering while others are just starting to get hit.
All my state corporations have contracts with each other, so my country hardly noticed.