Too complex, I remember you before with hack detection. Try this avrona.
summon Pig ~ ~ ~ {CustomName:Random,NoAI:1}
Do this, and next to it summon another, and after that keep going. One pig for every possibility.
From There, use the following command:
execute @r[type=Pig,name=Random] ~ ~ ~ setblock ~ ~-1 ~ redstone_block 0
This makes a random pig put a redstone block below them, and with command blocks resetting that can be a good randomizer. Each redstone block will have a setblock air to reset it, and the redstone block will also set off another command block, doing whatever you want for each possibility.

Let me know if its unclear.
Tedk

bump

bump

EDIT: My bad, I only read the rest of the post now. This gives you a random number, but not a random redstone output. You will need to add on extra command blocks to get your desired redstone output.

And what is that command?

Also just for your information, I want to use this system for a treasure system for my server.

avrona

Use a dropper; have a cobble block and a sword. The reason is because they have different comparator output strength.

So have the dropper shoot into a hopper; it will pick a random item from the dropper. Then have the hopper point to a dropper under the first one, and have it point up. That should give it enough time to take the signal. Then put a comparator facing out of the hopper. Then you can mess with locking the signal if you want to have it as a long output strength. Then do a comparator clock to reset it. Should look like this:

I don't really get that. The pictures aren't really clear and are also tiny. Also how many different outputs does it have?

Click on them and it will make them bigger, sorry about that.
It has 2 outputs, but you can have multiple randomizers hooked up to one another

EDIT: My bad, I only read the rest of the post now. This gives you a random number, but not a random redstone output. You will need to add on extra command blocks to get your desired redstone output.

You can use command blocks' @r feature.

Firstly, create a scoreboard objective. It will be a dummy objective. I'll be naming mine RANDOM.

Summon a few invisible armorstands and name them each differently. (In example: Random1, Random2, Random3....). Now make sure all of these armorstands have the same tag. I'll be naming this tag Open.

Whenever you want to randomize the score of RANDOM, use this chain of commands:
/scoreboard players tag @r[type=ArmorStand,tag=Open] add Picked

A little bit of delay later: (1 tick is fine for conditional chain command blocks, but 2 ticks are required for comparators.)
/scoreboard players tag @e[type=ArmorStand,tag=Open] remove Open


You will now need 1 repeating command block for each of your armorstands.
/testfor @e[type=ArmorStand,tag=Open]

Add on a conditional chain command block:
/scoreboard players set Dummy RANDOM [NUMBER]

If you want the random number to apply to a certain player/mob instead of globally, replace Dummy with your selector (@a,@p,etc).

To make this mulitplayer compatible, try adding on extra systems, or more advanced, have the triggering player/mob spawn armorstands onto themselves the randomizing armorstands.

Pros:
Fast
Reliable
Uses no redstone (only command blocks, if you chose to use conditional chains)
Easily expandable

Cons:
Uses command blocks
Uses entities

Use a dropper; have a cobble block and a sword. The reason is because they have different comparator output strength.

So have the dropper shoot into a hopper; it will pick a random item from the dropper. Then have the hopper point to a dropper under the first one, and have it point up. That should give it enough time to take the signal. Then put a comparator facing out of the hopper. Then you can mess with locking the signal if you want to have it as a long output strength. Then do a comparator clock to reset it. Should look like this:

I don't really get that. The pictures aren't really clear and are also tiny. Also how many different outputs does it have?

Use a dropper; have a cobble block and a sword. The reason is because they have different comparator output strength.

So have the dropper shoot into a hopper; it will pick a random item from the dropper. Then have the hopper point to a dropper under the first one, and have it point up. That should give it enough time to take the signal. Then put a comparator facing out of the hopper. Then you can mess with locking the signal if you want to have it as a long output strength. Then do a comparator clock to reset it. Should look like this: