I'm sorry if this is a stupid question or has been asked before. I just wanted to know if any and all DDR4 laptop ram sticks will fit into my laptop which already has one 8GB DDR4-2133 SDRAM stick in it. I just wanted to buy another 8GB ram stick. Is it safe to assume that even though they look different, that they're all basically the same and would fit? Also, does it matter that I'm using different brands or does my set need to be the exact same make and model? Thanks in advance for the response guys.
https://www.amazon.com/Kingston-Technology-HyperX-2133MHz-HX421S13IB/dp/B014R8JPYW/ref=sr_1_2?ie=UTF8&qid=1467994845&sr=8-2&keywords=ddr4+ram+laptop
https://www.amazon.com/Kingston-Technology-ValueRAM-2133MHz-KVR21S15D8/dp/B015CVEOOO/ref=sr_1_8?ie=UTF8&qid=1467994845&sr=8-8&keywords=ddr4+ram+laptop
https://www.amazon.com/Kingston-Technology-ValueRAM-Notebook-KVR21SE15D8/dp/B012AXJA8C/ref=sr_1_10?ie=UTF8&qid=1467994845&sr=8-10&keywords=ddr4+ram+laptop
https://www.amazon.com/Kingston-Technology-HyperX-2133MHz-HX421S13IB/dp/B014R8JPYW/ref=sr_1_2?ie=UTF8&qid=1467994845&sr=8-2&keywords=ddr4+ram+laptop
https://www.amazon.com/Kingston-Technology-ValueRAM-2133MHz-KVR21S15D8/dp/B015CVEOOO/ref=sr_1_8?ie=UTF8&qid=1467994845&sr=8-8&keywords=ddr4+ram+laptop
https://www.amazon.com/Kingston-Technology-ValueRAM-Notebook-KVR21SE15D8/dp/B012AXJA8C/ref=sr_1_10?ie=UTF8&qid=1467994845&sr=8-10&keywords=ddr4+ram+laptop