Hi TinHa,
Go to your SSO Configuration and click on your AD that you have configured under identity source. You have to make it as default domain by clicking on the blue symbol that looks like this
Once this is done, Try logging in with your AD administrator and see if the inventory is populating.
If its still not, login into vCenter using the vSphere client and click on your vCenter object, go to the permissions tab and add permission with your AD user and the Administrator role. Now you should be able to login with the AD user to web client and the vCenter+inventory should show up.
Let me know if it works.