Review on PEMENOL DC-DC CNC USB Step Up/Down Power Supply Regulator Module: Adjustable Boost Buck Voltage Converter with Digital Display Voltmeter Ammeter and Battery Capacity Tester by Javarie Brumfield

At first I thought it was a dual voltage USB power adapter. I thought this would be ideal as a +/- power supply for op amps. This confusion was due to the picture. Unfortunately it's only voltage, but I was able to use it on a USB power supply and apply a "negative" voltage. So in the end he does what I want him to do. I also found out later that it also measures volts/amps if you need to monitor project load or battery performance. Pretty handy and a lot easier than the two voltmeter approach. When I read (Output -), (Output +) and (collectively) on the front of the unit I just assumed it was dual voltage and that was the source of my confusion. Maybe they can refine that on future models? So if you need a +/- margin, take two, worked for me anyway.