There are passive power factor correction methods for power supplies, but they usually are integrated into the front end. Other than a very large series inductor, there is nothing "reasonably simple" that can be done external to the supply.
Adding that much inductance to a full wave rectifier will cause it to average not peak filter.
With out inductor; 110Vin ac, 150Vout dc.
With inductor; 110Vin ac, 110Vout dc.
No, I'm talking about an inductor *before* the input bridge, in series with the incoming AC line. The question was about doing something simple, and I took that to mean something outside the purchased power supply.
I think the choke will "soften" the peak current.
The purpose is to have current flowing for most of the cycle. This will stop peak rectification.
Here is a pdf. It has a passive PF circuit that I have not used. see page 5. I have used boost PF circuits. https://ac-dc.power.com/design-supp.../an-53-active-power-factor-correction-basics/