If you have X cap and you try to put >X into it, it will most likely return errors. The mobo has to support the hardware, otherwise it returns errors. I've tried to put a 1024 stick into my sister's PC but the mobo couldn't handle it, despite saying it supported one type of 1024, this wasn't it.
I'm guessing you'll just get error beeps on boot-up. You need to check the documentation for your motherboard and only put RAM in it that it can accept.