How come while I am driving my 1996 Honda Accord the speedometer and radio will power surge?

Speedometer will be steady then quickly fall to about 10 mph then quickly shoot back up to the correct speed. At the exact same time the car radio will shut turn off and come right back on.
Car doesnt have any lose of steering or control. No problems starting either.

I've have the ignition switch replaced within the past two years.
I also think my alternator is within 3-4 years old.
Car has recently had other electrical problems such as the speedomter failing completely and being stuck at zero. Which I have had my shop replace within the past 3 months. Also my window switch broke around the same time.
So is there a likely cause for this? And could the old problems be related to this?
Added (1). power surge may be the wrong term. I just mean the speedometer and radio on and working perfectly but then suddenly turning off then right back on

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