If a Tax Liability is increased through an amended return, should the increased amount be added to original amount in order to report the complete 2017 Tax Liability?

yes. don't forget to include the amount already paid with your original filing. 
That way, it all works out.

Yes, the correct tax liability for 2017 is what was on the original return plus the Amended return.

If tax was due on the original return and paid, then the additional tax due is listed only on the Amended return.