I've got a bunch of 5V phone chargers from old cheap flip phones. I'd like to use one for my DRO project, but it needs to be regulated and fairly clean DC, not a charger which depends on filtering/regulation in the phone itself to clean up the power. I know some chargers are good DC and some not. This is one that does not just have a USB socket, but includes a cord to the phone. The legend on the charger does say 5.0V DC ... but is it good DC?
How can I tell without an O-scope to look at the output for noise? I do have a DVM. And/or is it possible also to hook up a headphone and just have a listen? If so I imagine I'd need a fairly high value resistor in series?
Or, any other ideas....?