I've used both methods. Honestly both will work. My issue with adding weight during the workout if you exceed the top of the range is that you might be able to hit the range on the other sets.
For example let's say with an all out effort to failure on the first set you are able to reach 11 reps. Personally when I hit failure I lose a few reps on the set after... so even if I stayed at the same weight I might only get 8 on the second set.
So if I add weight on top of that it might end up looking like: 11 - 7 - 5. Which is not the end of the world but the overall loading of the session might not be optimal.
The method of adding weight if you can exceed the top end of the rep range works well with lower reps (2-5) because you aren't accumulating as much fatigue so you should have too much drop-off between sets. This is what I recommended with cluster sets in which I have people do 3-5 reps... if they can do 6 reps, add weight on the next set. But if using higher reps you would likely have too much of a drop off in reps from set to set.
See two things happen when you so a set: activation and fatigue.
Activation: producing force activate/potentiate the nervous system; increasing your capacity to perform in subsequent sets. The more force you have to produce the more you activate the nervous system.
Fatigue: you burn glycogen, fatigue the muscle fibers, accumulate waste products that make it harder to contract the muscle; the result is that your capacity to perform on subsequent sets decreases.
If activation exceeds fatigue you can become stronger from set to set. If fatigue exceeds activation you become weaker from set to set.
Heavier weights = more activation
Higher reps = more fatigue
Which is why when using low reps your first set is rarely the best one. The second and even sometimes the third are better.
And with higher reps the first set is normally the best one and you degrade from set to set.
Which is why intra workout adjustements in weight will work better with lower reps.