I wanted to chime in here, this may or may not directly answer the initial question, but solved it for me and should be helpful for those looking to use remote IPMI with Dell R740xd or similar server using iDRAC9. Since I landed on this question in my search, I expect others will to.

In the Web iDRAC go to "iDRAC Settings"/"Connectivity"/"IPMI Settings." This can be simplified by searching for "IPMI Settings" in the upper right hand Search box. Make sure "Enable IPMI Over LAN" is "Enabled." Set your privilege as needed, for me it was "Administrator." Then either set the "Encryption Key" or copy it; this is needed for the command below.

You also need a valid iDRAC Username and Password, it does not work without these. For me I used the same credentials(root) I use in the iDRAC to login, but I expect you could add a specific user for IPMI if desired. The main points are that iDRAC9 IPMI uses "lanplus" as the interface, requires a valid User&Pass and the configured encryption key used as the "hex_key" in the ipmitool command.

ipmitool -I lanplus -H "hostname or IP of iDRAC" -U root -P "your passwd here" -y "encryption key from iDRAC" power status