Bad psu?

[robustus64]

Hello,
Ok guys iv been repairing computers for about 10 years.Ive recently had a chap bring his box in dead.So i check psu tests good using a psu tester digital type but power and reset switch are dim and flickering.Ive replaced mb and still no fire on lights or fan this is third board.. ANyone ever have a psu test good but is still bad somehow?

 

[hairystuff]

I've had a few cheap psu test good with a tester but under load it would flickker on for a split second then off and not turn on again until the power cord was removed and reinserted after 10 seconds, the only way I could get it to fire up was by holding the reset and then pressing power, then releasing reset once the HDDs spun up.