Having a motherboard Z370 w/the latest bios 2.2.0 it should be possible. I mean all other Z370 boards take 9th gen CPUs, why Dells shouldn't? Right?
Here is the BUT... I found out that if you have an i5-8400 like me, the motherboard may not take 9th gen CPUs... thus why I am here, trying to find a definite answer.
PS:I am running a 700watts PS and a GTX-1080ti. So I have power cover and I will be willing to get an upgraded cooler for the new CPU. When I game, all the stuff I am running on the background is getting the CPU to over 90% at times.