Hi,
I am using 19.5V/4.5A power supply, measured the Ripple Voltage across the load It is almost 140mv ,After 10min again i measured Ripple voltage on same load its reduced to 40mV How is it?

 

I would guess that the load current diminished after 10 minutes.

 

Putting it another way, the question cannot be answered unless/until the load is known when the ripple measurement is made.

 

Switching or linear supply?

How much warmer was the power supply after 10 minutes?

ak

 

I am using 19.5V/4.5A(Laptop adapter) switching power supply only,For Load purpose i am connecting 100ohm/10W wire wound resistor,The load is only getting more heat,For ur reference i attached ripple waveform details

 

Has the power supply been out of usage for a long time before these tests? If so, the output filter caps may have "deformed" and after a while, "reformed" to a proper value. Electrolytics can sometimes behave like that. It is not uncommon to connect replacement electrolytics that have been in storage to a slowly increasing volgtage up to near the rated voltage of the cap. This allows the electro-chemical reaction needed to form the dielectric barrier.