There's an option in the toolset that allows you to fool Caesar into believing that you demolished just one generator, which allows you to stay friendly with Caesar, while at the same time retaining the Securitrons. I was fixing some bugs in the toolset, noticed this option and was sure it was in-game as well, but now it seems it's cut content, because the only dialogue line that Caesar has is " felt the ground shake a while ago. I'll take that as a sign you got the job done," which he says regardless of what you did in the Vault. But this doesnt even make any sense, cause the possibility to create a divertion explosion to fool him has been cut, so there WAS no explosion, at least if you didn't blow up the Vault, so maybe he imagined it, hmm? Either I am overlooking something or this doesnt make any sense. If Obsidian didnt have the time to complete this, they should have at least introduced a Bluff option with Caesar or something, Speech skill to fool him, but not like this! I wanted to fix it, but I don't have any voiceover and nothing for this sort of thing. I mean, he must react SOMEHOW to the fact that there was NO explosion! I think the appropriate thing to do is to set the player hostile to the entire Caesar faction if player upgrades the Secs instead of demolishing them. Obsidian probably didn't do it, cause it would be frustrating, and they are right, but the current way simply doesnt make sense to me and is frustrating either for this reason. If Caesar doesnt give a damn about anything, question is why have I even been invited to him...

-Caesar wants me to destroy this place.
Was that meant to be a shocking revelation?
Of course Caesar wants it destroyed - he's afraid of what the bunker might hold, and rightly so.
But you're not going to do that. You're going to do the smart thing, and work for me.

-Caesar will kill me unless he believes I blew something up down here.
I see - you're in a predicament.
Just off the turbine room down below are three power regulators. It's a redundant system - only one is needed.
Go ahead and destroy one. The explosion will be large enough to be heard and felt aboveground.

-What if I destroy all three?
{lying}The bunker will be destroyed, and you'll die instantly.

Quest objecive updated:
(Optional) Fool Caesar by setting off an explosion in the Vault without destroying Mr. House's technology.