I have an Arduino Maker WiFi 1010 connected to three HC-SR04 ultrasonic rangefinders. When I plug the Arduino into my USB Hub (NOT powered), it correctly reports a distance of approximately 80 inches when pointed at the wall. This is extremely consistent across sensor readings.
But, when I unplug the Arduino from the computer and plug it into a wall wart (output is 5V 2.5A), the sensors start spewing seemingly random numbers for long distances. If I put an object close to the sensors, it seems to get a correct reading within 1ft, but less reliably than when it's connected directly to my USB hub.
My sketch reads each sensor 5 times, with a 60ms pause in between every reading, and a 60ms delay between each sensor. This works really consistently on the USB hub power, but seems to be much less consistent on anything else.
Is there something I'm doing wrong here? I am not an electrical engineer (in case that wasn't obvious!)