Do you mean a USB - UART bridge? Theses can usually not supply the current needed for an ESP32. You can try to add a large capacitor close to the WROOM module betwee4n 3V3 and GND.

I figured the breadboard supply would at least handle it, but the esp.osdebug output below shows I have a brownout, so you're probably correct. Perhaps the supply plus a larger cap together.

@robert-hh what power supply do you use? I added a 0.1uF ceramic and a 330uF electrolytic in parallel 10mm from the ESP32 module but it's still happening. Breadboard power supply has an AMS1117-3.3 with additional 100uF electrolytic. Regulates down a 12V 1A wall wart.

I just have ready-to-use boards from Wemos or epsressif with USB insterface, which take poer from USB and an on.board regulator. The AMS1117-3.3 should deliver sufficient current- It may not be the fastest regulator, but the cap close to the WROOM module should handle that. And it's used in that context.
Did you connect all GND pins of the WROOM module?

Indeed I did connect all three GND pins of the WROVER, and I used big beefy 0.8 mm/31 mil traces for GND, 1 oz copper on the PCB. Tried a third breadboard power supply and even a 10A bench power supply, same problem. My working DevKitC also uses an AMS1117. The resistance of the custom PCB between 3.3V and GND is 13.5kOhm so it's not idling with excess current.

That was the problem. There's definitely a problem in the PCB design. I connected the bench power supply directly to the bypass cap leads that I had soldered on and can now start Wi-Fi without crashing. So, something is wrong in the PCB design.

Very good. That told me that I'm experiencing a brownout. I think @robert-hh is correct, it's either power supply and/or it needs a larger bypass cap.

I BOD: Brownout detector was triggered