Yes I did press the reset button. I can even measure 5V at the USB Port when the power supply is connected to 5V/GND pins. I can also measure continuity between the USB 5V pin and the other 5V pins...

I guess it's a software issue... I'll try upload another program

Thanks for the help!

edit: PlatformIO doesn't find the device... it's not at /dev/ttyUSB* like the m5Stick
edit2: I didn't read this before I ordered...

Note: The newly updated C3U shares the same features as C3, but the difference is that M5Stamp C3U without the USB download chip and the program download method is different (The C3U uses the ESP32-C3's built-in USB Serial for program download)

So I have to figure out how to make that work...

edit3:
OK I figured it out, I think. You have to hold the G9 button while the chip powers on (push reset or plug in power) to enter USB CDC mode. Then this platformio.ini worked for me:

[env:m5stack-stamps3] platform = espressif32 board = esp32-c3-devkitm-1 framework = arduino upload_port = /dev/ttyACM0 monitor_speed = 460800 build_flags = -D ARDUINO_USB_MODE=1 -D ARDUINO_USB_CDC_ON_BOOT=1

After uploading once, because of the "CDC_ON_BOOT" option, it goes into the CDC mode automatically without holding the button.