Three things to keep in mind: What's the power supply rating recommended for the specific card you want? The Inspiron 3668 specs don't list the PSU rating, but I suspect it's 240 Watts.  Does this card have the right video output ports for your monitor? You do not want to use VGA which is a low quality analog signal. Make sure the card supports the game(s) you want to play.  Looks like this card supports DirectX 12, but the "feature" level is only 11_0, which could be a problem with newer DirectX 12 games. Other than changing Secure Boot and correctly installing the card in the PCI-e x16 slot, you may have to load the driver if Windows Update doesn't do it for you. 
I have a inspiron 3668 and I am buying an asus 730 GDDR5 2gb. I saw from other forums that I need to take secure boot off and do some stuff in bios or my pc wont boot and im wondering if any of that is true an if so, how would I set it up.  [URL] Heres the link if it helps. Thanks
Dell Inspiron 3668 i3 7th gen gpu upgrade questions