Actual Cost (there is no "Real Cost" field in the english version of MS Project) is NOT the same as ACWP (Earned value "AC (CRTR)"). The difference is that "Actual Cost" is a single field and "ACWP" is a TIMEPHASED field (like all the earned value fields). This means that "ACWP" is calculated considering the project's "Status Date" (or the current date if "Status Date" has no value).
For example: suppose we have a 2-week, $1,000 task that starts on Monday, Nov. 6th, and finishes on Friday, Nov. 17th. Now suppose I update the project at Monday, Nov. 13th, marking the task as complete (100%) and changing "Actual Cost" to $1,500.00, but I do not update the finish date and let it with its original value (Nov. 17th).
Since today is Nov. 13th, the task SHOULD have a 50% advance, so "ACWP" will be $750.00!! Yes, even if the task is already at 100% and actual cost is $1,500.00!! (Oh, and "Cost Variance" will be $250.00 since "Planned Value" at Nov. 13th should be $500.00).
Now, let's play a little. If I change "Status Date" to a value later than Nov. 17th, then the task should be finished (according to the captured info). "ACWP" will be $1,500.00. If I change "Status Date" to a value earlier than Nov. 6th, then the task should not have started, and "AWCP" will be $0.00.
As you can see, Earned Value fields are calculated considering the project's status date, and reflect the value those fields should have that day. This way, you can change the status date and get the EV values corresponding to the selected date. This is really, really useful.
I bet that, in your file, the status date (or the current date, if you haven't changed status date value) is a few days before the actual finish date of the task, so "AC" reflects a value that is a little lower than Actual Cost.
Hope this helps. Greetings.