I'm not sure if I'm the one doing something wrong, but everytime I tried to use a field that require a short tag, it seems ignored while the rest work just fine.

Here is an exemple :

setblock ~ ~ ~ minecraft:mob_spawner 0 destroy {
    MaxSpawnDelay:1,
    RequiredPlayerRange:1,
    EntityId:Creeper,
    SpawnData:
        {
        powered:0
        },
    SpawnPotentials:[
        {
        Type:Creeper,
        Weight:2,
        Properties:
            {
            powered:0
            }
        },
        {
        Type:Creeper,
        Weight:1,
        Properties:
            {
            powered:1
            }
        }
    ]
}

Note : Since the chat can't handle more than 256 characters, you have to put this code into a command block and activate it with redstone to make it work.

This code is supposed to replace the command block by a custom spawner which spawn at first a normal creeper
(because of "EntityId:Creeper" and "SpawnData:

") and then randomly a normal or a charged creeper with weights of 2 and 1 respectively.

This part works fine but "RequiredPlayerRange:1" and " MaxSpawnDelay:1" seem ignored : the spawner keeps its normal range of activation and the delay between each spawning is default.