In general, yes, you should reproduce quotations as they appear in the source. If a quotation appears in all caps in your source, most of the time you should use all caps when you quote it. However, if a quotation is very long and also in all caps, it’s OK to quote it as if it were not in all caps, as long as the capital letters are not essential for the meaning. The following sentences provide examples:
In George Orwell’s 1984, Winston writes “DOWN WITH BIG BROTHER” over and over again in his diary (18).
The text behind the statue of Abraham Lincoln in the Lincoln Memorial reads, “In this temple as in the hearts of the people for whom he saved the Union the memory of Abraham Lincoln in enshrined forever” (“Lincoln Memorial Inscriptions”).
“Lincoln Memorial Inscriptions.” National Park Service, www.nps.gov/linc/learn/historyculture/inscriptions.htm. Accessed 21 Apr. 2023.
Orwell, George. 1984. Houghton Mifflin Harcourt, 2013.
In the first example, from Orwell’s 1984, the text “DOWN WITH BIG BROTHER” is reproduced as it appears in the book, in all caps. The quotation is short, and the capital letters are essential for the meaning, because they reveal the importance Winston places on the phrase. In the second example, the long quotation from the Lincoln memorial appears lowercase, even though the website that is cited presents it in all caps. The capital letters are not essential for the meaning and so can be changed to lowercase for ease of reading.