As the 3ds has no GBA slot I assume you mean the SD card that you wanted to use in the GBA slot supercard works in the 3ds but does not work on the other things you have.
First question. Is this a SDHC card (if it is 4GB or greater it will be)? As far as I am aware the supercard GBA slot offerings never supported more than SD format (2GB and under).
You say mini so I have to ask if it is a microSD to miniSD converter you are trying? For some reason micro to mini converters are awful -- mini to full SD and micro to full SD are fine and I have never had one fail that was not abused first, micro to mini on the other hand mostly want to be thrown away as soon as they are made as they are so bad. I don't know why but they have caused no end of hassle with devices on forums like this over the years.
I will leave it at that for now, however I will say the supercard GBA lineup is not great. If it is what you have it is what you have but if you can at all invest in a proper GBA flash cart it would be the thing we suggest doing.