Noise Spikes observed in testing circuits

[ku637]

Hi I'm doing a equipment integrated testing..
It has got two PCBs . Equipment has a 12V battery and One AC /DC supply generating 15V from mains, both are ORed and given to one board which generates 10V using buck and gives to other board.
Both the boards has got some microcontrollers and generates lower core voltages required for their operation..
For my testing im trying to see the performance of supply voltage levels during transition from battery to mains..

I'm doing this by turning ON AC supply and checking the core voltages for any issues using oscilloscope probing inside the system.

Unfortunately I'm observing some noise in microseconds coming on all the supply rails in oscilloscope during AC turn ON..
I feel like this is a noise problem since it's a microsecond noise on the voltage rails..

I tried shielded cable to connect to oscilloscope for probing but still it is observed..

Any idea to understand if the noise is really present or its being coupled to the oscilloscope probes..

Thanks

 

[kam1787]

Do not understand why you would OR the power supplies...........

Turn-on transients are common

You do not describe the AC/DC PSU..............