Testing PL2303 & USB-TTL Serial cable for 3.3V

I have to flash a TYWE3S module with tasmota. Ive flashed a esp8266 before using 3.3V from an arduino uno. So from what I understand the whole idea behind these 3.3V-5V converters is that these modules are so low power that communication must be done at 3.3V. So I want to check the voltage before doing so, but Im not entirely sure how these converters work.

PL2303 |500x500

When I measure 3.3V pin against GND pin I get 3.50V. When I measure 5.0V pin against GND pin I get 5.15V. When I measure Tx or Rx against GND pin I get 5.15V.

So this means this module will fry my TYWE3S?

My USB-TTL cable: |500x500

When I measure red Vcc pin against GND pin I get 5.16V When I measure green Tx pin against GND pin I get 3.62V When I measure white Rx pin against GND pin I get 0V

Both of your pictures show up as big red X so find some other way to post pictures.

Most of these USB serial devices output 5V straight from the computer USB port on the pin labelled 5V or VCC. The Tx/Rx are usually designed for 3.3V logic levels. Measuring the Rx with nothing attached may have random or 0V. The Tx should have 3.3V. It is not unusual for the voltages to be +/- 10% off the ideal values.

So there is no real way of testing them?

Use one of these https://www.tinyosshop.com/index.php?route=product/product&filter_name=ftdi&filter_description=true&filter_sub_category=true&product_id=600 The jumper selects whether the IO is 3.3V or 5V.

Use one of these https://www.tinyosshop.com/index.php?route=product/product&filter_name=ftdi&filter_description=true&filter_sub_category=true&product_id=600 The jumper selects whether the IO is 3.3V or 5V.

|500x246

They dont have jumpers.

It ends at a female header, use some male-male, or male-female jumpers to connect to your device. https://www.tinyosshop.com/index.php?route=product/product&product_id=405