I was looking at a breadboard power module (link). This board has two inputs: a DC plug (7-12V advised) and a USB mini (5V). Using either of those two inputs, the board provides two voltages (3.3V and 5V) using fixed AMS1117 voltage regulators. So far, so good.
However, looking at the module, and after some path testing with a multimeter, it seems that something strange is happening. When using the USB as input to power the module, the 3V3 regulator gets its input through the 5V regulator. But in a strange reversed way. (The voltage at the input pins of both AMS1117's is around 4.5V.)
Using either DC or USB as input power, both 5V and 3V3 rails are working. But I suspect that the 3V3 rail using USB as input power, might not be a proper supply.
Am I correct in assuming that this reversed use of the 5V regulator to power the 3V3 regulator is less than desirable? Or am I missing something?