I don't know exactly what this saying mean, but I can, off hand, think of a few real-life applications that might help us to a conclusion. For example: by "silence," he could mean secrecy. Now, who is labeled as "secret"? The CIA is a secret agency in their actions. OK, bad example. Let's move on to Area 51, a "secret" military base out of New Mexico. Their idea of secret is going public. How they do this is to let people ask certain questions and then the government will tell them that they can not answer either way. This automatically makes stupid people think that this means the government has something to hide. Pretty soon, people start building their own theories of what goes on at Area 51, theories built without facts. What happens next is that people just focus on why their theories are right, instead of searching for facts, effectively ignoring Area 51 (in reality).
That is true power; the power to do whatever you want, morality not-withstanding because the general public has no clue of what you are doing. This is a perfect example of "keeping secrets public." Yes, that is an oxy-moron, but I can get away with it because society is full of morons, and I understand that. I won't allow myself to become one of them as I study the poor creature called "society."
If you want more reference, know this: the US anti-terrorist group known as the NAVY SEALs are probably the most demanding and well-trained group of the western civilization. The only reason that the U.S.M.C. Recon, Green Berets, and perhaps even the Marines themselves are bigger in publicity is because we know what they do. We have seen their victories, and they were good. The SEALs, however, have victories that must remain unknown. They officially don't exist, and they like to keep it that way for the obvious reason; "Silence is the ultimate weapon of power." They are powerful, that is undeniable, but the one thing that makes them more powerful than others (in my opinion) is the fact that that can keep their mouths shut. We, being the general public, know that groups like DEV GRU and SEAL Team 10 exist, but we don't have a clue as to where they go and what they do. This makes them more free to their actions and definately more powerful.
My only other theory on this controversial matter is a little similar. The other kind of silent power is the kind that builds up, well, silently. It is the waiting time bomb inside a person, a group of persons, or a whole nation. It is the power that lies dormant, unused and unnoticed until it gets so great that it bursts out with a devestating mix of surprise and destruction.
A good example of silent power on a personal level is in the novel "Shane," by Jack Schaeffer. The book is about a mysterious, wandering, and yet charming man who would befriend you even while you knew he was dangerous. He wasn't dangerous to everybody, he was statistically safe, for that matter. We know that every man has his demons, and when the right people got under Shane's (the wanderer) skin, they had unknowingly opened the gates of Hell upon themselves. This is the kind of silent power that is the most dangerous.
If turmoil is held inside, with no way to slowly vent out, then it will build to a critical point, and you will have all of that hatred, anger, sorrow, fear, or whatever other emotion I have yet to experience suddenly washing over you in ten fold what it originally would have been. It's like the Plutonium bomb compared to Hiroshima. Just think about what would have happened if that war dragged out longer.