2004 Volvo XC90 bizarre power and engine failure 2004 XC90

On a 6 hour drive to Los Angeles, my 69,000 miles, 2004 Volvo XC 90 experienced a severe "thump" in the front end, which was then followed by a very brief (split second) internal (meaning dashboard lights, hi-fi, dome lights, etc) power failure. Initially, the power failure would last only a split second and then car would continue running as normal, and there we no error codes or check engine lights. This happened as many as five times in a 6 hour drive.

But on the last long drive home, the "thump" was harder than usual, and the lights internally completely went out, hazard lights could not be turned on, blinkers could not be switched on, hi-fi went out, etc (though the electric windows would work).

I pulled over, and turned the car off and restarted it, and the yellow exclamation point dashboard icon/alert lit up, and a service message flashed referring to the anti-lock brake failure, and that the SRS needed to be checked.

I have it at another dealership in Northern California, who seems equally mystified and have told me that they dont think the error code of check the SRS is going to fix the problem.

Any advice you can offer would be appreciated. Thx, Brad