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I think there is no resonance in DC power input circuit because for resonance to occur, voltage and current must be in phase but in DC power input circuit voltage and current can't be in phase. Is this right?

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    \$\begingroup\$ You have to define what you mean by that. For example you can have a DC circuit that consumes no current and then turns on and consumes a lot of current, so there are transients. A microcontroller that runs at 1 MHz will gulp surges of current at 1 MHz, so unless you are careful, there may very well be resonances and the supply is not DC any more. \$\endgroup\$
    – Justme
    Sep 19 at 12:49
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    \$\begingroup\$ Could well be resonance especially if you stick a ferrite bead in there blindly. \$\endgroup\$ Sep 19 at 13:13

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Phase usually applies to sinusoids, but could apply to any periodic waveform. A dc voltage is not periodic, so phase does not apply.

Resonant behaviour is based the polar angle of impedance, which is set by frequency. The phase of voltage and current is a consequence of frequency and the impedance. While resonance can result in equal phase, equal phase does not guarantee resonance.

Power supplies are often stabilized by a feedback controller. If the stabilization circuit is insufficient then resonance may be observed.

If you mean by “power input circuit”, the circuit that the power supply is attached to, then the circuitry can resonate. The input filters may resonate if not properly designed.

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Resonance can happen and could damage the power supply input. The DC power input of many devices has an input capacitance. The conductors feeding the input of the power supply pin have series resistance and inductance. The inductance and capacitance form a resonant circuit which can ring excessively if the conditions are right when power is applied or there is a step change in current. The following is a LTspice simulation showing excess ringing. To tame this, a lossy capacitor (capacitor with high ESR) can be used.

enter image description here

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