I understand that CO2 is a clean agent extinguisher, but being too cheap to buy a proper A and C rated clean agent such as FE-36 or Halotron 1 for a switch gear room seems pretty irrational to me. Such locations don't even call for a B rating.
At home, I have used ABC drychem extinguishers to put out fires (two disposable ones saved a neighbor's house from being completely destroyed, though a similar fire did take it 6 months later). They work, and they work quickly. I happen to have a pair of Halon 1211 extinguishers I sort of inherited, as well as a pair of CO2 extinguishers in my garage, but have never even considered reaching for one.
In other capacities that I am not at total liberty to discuss in detail, I have been involved in the aftermath of the use of an ABC drychem in a facility filled with sensitive equipment. From that situation, I can say with absolute confidence, that the damage caused by the dry chemical powder was absolutely NOTHING compared to the damage caused by the smoke. Not even the slightest drop in the bucket. To give you a visual analogy to picture the spread of the damage from each in square footage, imagine that the drychem contaminated a hottub. Now imagine the entire water park around this hot tub being contaminated by the smoke alone. Plus, not only is the smoke more corrosive and pervasive, but it is also significantly harder to clean up as well.
So, think about this. Every SECOND that a fire is smoldering and spreading smoke, the smoke alone is causing more damage than the entire contents of an ABC extinguisher. If you just paused for a second to think about which extinguisher to grab, you're already losing. If you've spent a CO2 extinguisher and are reaching for a second bottle, you've lost big time.