Hello, burned all the sources ?, is a humid area where you are or the place is wet. Check that they do not have sulfate connectors that are usually responsible, I repaired several with that problem.
Buy two 4A or 5A sources only for the cameras, then connect 4 cameras per source. Use the pulpits so you avoid having to make splices. Then, give the DVR an individual source of minimum 3A. Keep in mind that the more amperage you give your teams the better it will be. These 3 sources connect them to a stabilizer, or if your budget allows it, to a UPS.
That way you shouldn't have any more problems. And now, take the opportunity to check how the connectors are, if you see that one has rust you can clean them by spraying them with WD40.
Luck!