I7-9700k has not been validated but it should boot just like the validated 9700. Caveat: you cannot overclock -k cpu due to 3470 chipset (and bios). You would normally need VRM heatsink to support -k cpu but since you cannot overclock or increase core V on cpu that recommendation is dropped. Most importantly the Dell stock heatsink is pathetically inadequate for -k cpu that has high TDP.  Lastly you may need a psu upgrade to support -k cpu depending on system configuration.