Does DELL Optiplex 3050 CPU upgrade to i5 8th CPU or i5 9th CPU?

I do not think so.  3050 has B250 chipset, so it only supports 6-7th gen Intel CPU.  8th gen intel CPU needs 300 series chipset. with bios update 300 series chipset can support 9th gen cpu too.  but not with 200 series.  Intel made it clear that 8th gen is not backward compatible.  they want you to buy their new motherboard if you want 8/9 th gen cpu.

Also:  Optiplex 3050 Spec Sheet