Always have multiple known good quality power supplies, and good cables (high current rated, and preferably short) , and try several of them first.
Also know that power supplies which worked perfectly for year(s) can an do go bad -- they still look like they work in majority in cases, but at higher load their voltage drops below
4.75V even for a shor time, and RaspberryPi reboots or some parts of it fail.
That happened to me recently, raspberry pi would sometimes lose ethernet connection until manual power cycle (reboot didn't help). With multimeter, I've measured the voltage between
TP2 test contacts while being at
4.9V most of the time, sometimes dropping as far down as
4.60V. Issue was power supply (rated at
2.4A which was working fine for two years and nobody touched it before things started happening). New power supply fixed it immediately.
Alternatively, it may be that one of your cameras is faulty and is driving more current that it should. If that is the case, and you have (or can borrow) third one, you can test them in pairs (
B+C) to isolate the faulty one.
If all of that fails, if you can get/borrow extra raspberry pi and/or sdcard, you can try to isolate if problem is in one of them.