I can't confirm any China access to transformers although I can't rule it out.hence why strategic importance of NOT allowing CCP access to our electrical grid.
those HUGE transformers are already installed with embedded electronics.
my guess is CCP needed access to activate remote control to those transformers.
which Biden granted CCP access to America's grid in his EO on his first day.
Most are pretty dumb intelligence wise. The control systems typically reside beyond bluetooth or wifi range and are hardened against intrusion.
Our Control Systems when I worked at OG&E Sooner Power plant has zero access to the internet. No need for firewalls or anything else although they were installed as a precaution for other reasons I won't talk about.