Today I changed a sql server service startup account during testing, then when I tried to connect sql server with powershell, I got error message below:

The target principal name is incorrect.  Cannot generate SSPI context."

Here is the troubleshooting step I used
1. Rollback service startup account to old one, then the powershell script work. so it should be the issue with the new account.

2. Start sql server service again with new account. check sql server error log, then found error message in it

2013-01-20 00:53:36.49 Server      The SQL Server Network Interface library could not register the Service Principal Name (SPN) for the SQL Server service. Error: 0x2098, state: 15. Failure to register an SPN may cause integrated authentication to fall back to NTLM instead of Kerberos. This is an informational message. Further action is only required if Kerberos authentication is required by authentication policies.

1. Click Start, click Run, type Adsiedit.msc, and then click OK.
2. In the ADSI Edit snap-in, expand Domain [DomainName], expand DC= RootDomainName, expand CN=Users, right-click CN= AccountName, and then click Properties. 
3. In the CN= AccountName Properties dialog box, click the Security tab.
4. On the Security tab, click Advanced.
5. In the Advanced Security Settings dialog box, select one of "SELF"'s row just like the pic below

     6. Click Edit, Open Permission Entry dialog box.

     7. Make sure Pricipal is "SELF", Type is "Allow" and "Applied to" is "This Object Only", in Properties section, select the properties below:

Read servicePrincipalName

Write servicePrincipalName

     8. Click OK three times, and then exit the ADSI Edit snap-in.