I found a better solution,
In the player, you know how the pass on the filters turn the switch on?
Use the fail on the filter to turn the switch off.
This way you wont have multiple power-ups going off.
If your asking if there is a way to make the random more random, I suggest using a bigger number (preferred to be even of the multiple of 3).
Such as 9, us a filter less than 4 for one, use 2 filters with greater than 3 and the other is less than 6, and use greater than 6 for the last filter. This way the number is random between 1 - 9 with 1 - 3 to the first power-up, 4 - 6 to the second, and 7 - 9 for the last power-up.
More numbers = More random numbers generated