As long as you don’t tell us what you want or which problem you want to get solved, I cannot give you any advice.
Before you are going to buy an NVMe SSD (e.g. a Samsung 970 EVO) and additionally an M.2>PCIe adapter, you should check, whether the BIOS of your Dell system supports booting off an NVMe SSD, but this discussion would be completely off-topic.