CP2102 are pretty good ones and never let me down :-) Is your UART connection to ESP32 working correctly? Can you see the boot message and whatever happens next in terminal (cu / minicom)? Are RX TX pins not swapped? Power supply okay?
Are boards generic devkits of custom hardware? ESP32 in addition to RX TX needs two control lines Reset and Boot that will switch the chip to bootloader / flashing mode. Most USB-to-UART use RTS/CTS lines for that. Are you sure these lines are available on your board and connected to the target correctly? Do you have Reset and Boot buttons on the board so you could trigger bootloader by hand (hold Boot, press and release Reset, device will be in bootloader upload mode, retry esptool flashing now). You can also play with the buttons with active terminal attached (i.e. minicom) to see if they work as expected. Minicom serial terminal is pretty cool as it allows you to watch UART behavior on adapter (un)plug. In minicom you can also enable/disable hardware flow control lines (Ctrl+A O -> Serial Port Setup -> (F) Hardware Flow Control). You can switch that easily and watch the target behavior. If this is the problem you may want to use stty (1) to enable/disable hardware flow control on the port. Can you try with another board? ESP32 has fuses that may permanently disable and/or mess up some hardware features. -- CeDeROM, SQ7MHZ, http://www.tomek.cedro.info
