[Python] pandas- merge to datasets with diff col names adding values from the second into the...

I have a couple of dataframes:

DTime A B C
2023-02-21 00:00:01 0 0 0
2023-02-21 00:00:02 0 1 0
2023-02-21 00:00:03 0 0 2
2023-02-21 00:00:04 4 2 0


DTime AAA BBB CC DDD EE
2023-02-21 00:00:01 0 0 0 1 0
2023-02-21 00:00:02 0 1 0 0 0
2023-02-21 00:00:03 0 0 2 0 1
2023-02-21 00:00:04 1 0 0 0 0


I need to merge the first into the second where I explicitly map the cols and sum the values. i.e. - I want A to sum into AAA, B into BBB and C into CCC:

DTime AAA BBB CC DDD EE
2023-02-21 00:00:01 0 0 0 1 0
2023-02-21 00:00:02 0 2 0 0 0
2023-02-21 00:00:03 0 0 4 0 1
2023-02-21 00:00:04 5 2 0 0 0


I can't seem to make this happen without going line-by-line... But there must be a better way since I have thousands of rows and hundreds of cols.

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