Wall supply Plug-in "noise"
The first scope trace could be a measurement artifact:

When you plug in the wall supply, a large inrush current will charge the input caps. There will also be a current spike through the primary-to-secondary capacitance. This could cause some common mode noise which could be displayed by the scope as an actual signal. Also your probe's ground clip may pick up some of th magnetic field due to the capacitor charging current.
If the input supply voltage was probed on a capacitor, especially a ceramic capacitor which has low ESR and inductance, these high frequency +/- 5V oscillations would look suspicious.
Think about the current that would have to flow in a 100nF ceramic cap to get voltage to spike up by 5V in one scope pixel, say 200ns at 2µs/div. That's more than 2 Amps! Pretty unlikely.
I'd recommend not using the scope probe, and soldering a coax to the input ceramic cap instead, with a 50R resistor in series. Also place a ferrite sleeve on the coax, set the scope to 50R input impedance (make sure it can take the DC voltage), and measure again.