12V 24V to 5V 6A 30W Dual USB Female DC Buck Converter Adapter Step Down Module

A RaspberryPi 4 power supply is 5.1V / 3.0A DC. The 6A output sounds perfect for powering 2 rpi4s, and I check with a multimeter and the 5V output is indeed 5.1V. This should work, and yet I get this in my kernel logs: Jul 08 12:57:19 raspberrypi1 kernel: hwmon hwmon1: Undervoltage detected! Jul 08 12:57:32 raspberrypi1 kernel: hwmon hwmon1: Voltage normalised No resets or performance problems, just the log messages. UPDATE: After some time, I remembered that the micro USB cable I'm using is not rated for that amount of current. If i use a good cable it works fine.

Product works as intended - voltage consistency is questionable but works for my purposes

I wanted to use this converter to install usb charging ports in my car. But when connecting the converter to 12v, my phone would charge at 3 watts (super slowly), far from the 15 watts that is advertized per usb port. Charging speeds would probably slow down even more if I had plugged in a second phone to charge. Poor performance and very unsatisfied. Find a different step down converter.

Ordered the 30 Watt (6 Amp) version. It only outputs 4.2 Amps, or 2.1 Amps each USB Outlet. Tested with a multimeter, as well as my phone. Otherwise, it works.

This converter concealed nicely beneath the kick panel of my car, next to the cabin fuse block. I stuck it in place with silicone-gel velcro, and tapped power using a piggy-back fuse holder with a 5A fuse. Then I plugged USB-A extension cords into it to run to different parts of the car, where I had USB-powered device mounted (one by the rear-view mirror, and one on the dash). It made for a very neat installation, AND it didn't use up any power outlets in my car.

Using this to power a power injector for a bluetooth adapter and charging a laptop. Working perfectly for now, will update if any issues arise.

one of the USB ports stopped working