I connected a cheap wallwart to my new project but it did not work properly. The DC voltage from the wallwart was a little low so maybe something in my circuit was drawing too much current? I 'scope'd it and found TONS of ripple coming from the wallwart.
I cut the wallwart apart expecting to see a swollen filter capacitor but the capacitor was missing. There was a symbol and two solder pads for an electrolytic capacitor but the capacitor was not there. The wallwart is labelled, "9VDC/280mA, made in (you know where)". I added a 470uF/16V capacitor and measured 19V with no load so I quickly removed my 16V capacitor and used a 220uF/25V one. The no load voltage is still 19V but is 16V with 100mA of load so I changed the marking on the label to 16V/100mA.
I cut the wallwart apart expecting to see a swollen filter capacitor but the capacitor was missing. There was a symbol and two solder pads for an electrolytic capacitor but the capacitor was not there. The wallwart is labelled, "9VDC/280mA, made in (you know where)". I added a 470uF/16V capacitor and measured 19V with no load so I quickly removed my 16V capacitor and used a 220uF/25V one. The no load voltage is still 19V but is 16V with 100mA of load so I changed the marking on the label to 16V/100mA.