My assumption was that a brute force password guessing algorithm would basically only get a boolean result; it worked or it didn't. I don't understand how it could know it was partially correct unless somehow it had access to the encrypted password, but then I would think that you'd be dealing with an entirely different type of algorithm.
It depends on the type of attack.
If the attacker has extracted a hashed password table, a brute-force attack can run every combination of letters and numbers for a single password out to twelve or more characters lightning fast. Using this (dumb) method I could typically crack 500 passwords in an hour or two on my (underpowered) laptop. Using an AWS cluster or something similar, we could get the same job done in a second or two. This was legal, by the way, because I had written authorization from my customers to do it.
Using a good dictionary, we could cut the time by a factor of roughly ten -- instead of 120 minutes, maybe 12. "Correcthorsebatterystaple" passwords would fall quickly to this method. But we'd be back to the brute-force type of attack for a strong password like those I mentioned upthread.
Using rainbow hash tables, if we got hits we'd get the whole thing done in a few seconds.
If you're not working on extracted password hashes, but rather attacking via a user interface, things get much, much slower.