Power Supply Question : AC or DC First?

Thread Starter


Joined Aug 30, 2020
For consumer electronics, such as laptops, routers/switches, iPhones, and tablets, I would like to reduce the chances of device failure.

Some AC/DC power supplies look very cheap and untrustworthy, but in general, I tell people the same thing.

My advice is to always plug in the DC connector first and then plug the AC IEC plug in to the wall outlet. My reason is that the IEC plug has the longer ground pin and I would hope the AC/DC converter has some protection from spikes.

Is this good advice or am I mistaken for specific situations?


Joined Feb 24, 2006
That's funny I always do it the other way. I plug the AC in first and then connect the DC power. I guess I never really thought about it.


Joined Jul 18, 2013
It has been my experience that SMPS supplies do not have an earth referenced DC common, both Industrial and Domestic.
The exception of course, is tower PC's for e.g.