Thank you for the response. I was seeing things differently, but will rethink it again.
When I look at figure A, and imagine high frequency noise super imposed on Vcc from somewhere else, this noise would see a least resistance path through the cap rather than through the 100 ohm, and accordingly this RC setup will filter such noise from reaching the gray box.
While in figure B, I imagine some high frequency signal generated inside the gray box that may leak to the power supply then to other parts of the circuit causing oscillation (may be), so this leaked signal will see a low impedance C2 and go to ground rather than the R2 100 ohm.
The gray box is just a mic preamp as an example, it may be an oscillator, or an amplifier.