To clear up any confusion, I'd like to explain:
The sefer Tehillim with the segulot information is called Shaarei Rachamim and is published under the auspices of Zichron Rachamim by the rosh yeshivah Rav Aharon Zakai and distributed by Hasefer Hatov, which is located on Chagai Street in Yerushalayim.
(Rav Zakai heads the Ohr Yom Tov institutions and Talmud Torah Habayit Hayehudi, and has also published a multi-volume set on the Jewish home, among other books. To see the full list of his books, please click HERE. To see a list of his books with detailed descriptions, please click HERE.)
This Sefer Tehillim is titled: Sefer Tehillim: Shaar Harachamim im segulot v'tefillot haChida (with segulot and prayers of the Chida).
There are a lot of prayers and segulot from the Chida in the back of the book. The only reason why I wasn't 100% sure that the segulot mentioned with each perek were from the Chida is because in the back of the book, there is also the Tikkun Haklali of Rebbe Nachman of Breslov with the proper instructions and the usual verses of preface and conclusion-- except that it's not called Tikkun Haklali but "Tikkun Hakeri rachmana latzlan," AND it doesn't say anything about Rebbe Nachman. So it made me wonder whether ALL the segulot mentioned in the book are from the Chida or whether some are from another great sage, but the compilers simply didn't think to add the sage's name.
I hope that all made sense.
Anyway, the good man who answered the phone very nicely explained that if the book says that the segulot are from the Chida, then that means ALL the segulot within are from the Chida. He also explained that the Tikkun Haklali wasn't specifically credited to Rebbe Nachman because "everyone knows" it's Rebbe Nachman's Tikkun. He seemed surprised that anyone might think it was put together by anyone else.
(To my mind, this is a particularly interesting cultural variation. Just like your average English-speaker knows that "To be or not to be" is Hamlet by Shakespeare or that any TV-watching American from my generation knows that "Where's the beef?" is a Wendy's commercial, so too a Sefardi Israeli interested in reciting Tehillim with the Chida's segulot would certainly know that the Tikkun on the last page is the famous Tikkun Haklali by Rebbe Nachman. This cultural assumption makes sense within their cultural framework, even though it doesn't within my cultural framework.)
The person with whom I spoke didn't know the exact source in the Chida's writings for each segulah, but gave me the number of Rav Zakai for more information. If I get up the gumption, I'll call the rav (or more preferably, convince my husband to do it) for further information.
Okay, I hope the above helps anyone with the same kind of inquiring mind!
Thanks very much to the astute readers who inquired in the first place.
To view or download the lists of segulot/uses of each Tehillim (not completed as of yet), please see the following:
The Segulot/Uses for the First 20 Chapters of Tehillim
The Segulot/Uses of Tehillim/Psalms 21-64
UPDATED: A List of Specific Tehillim for Different Ailments of Body and Soul