Electrical system/computer

My son was driving his s60 when it bucked(like hitting a speed bump at 50 mph) several times over 10 minutes when the instruments and panel light went out and he lost power and had to be towed to the volvo dealer. They kept it for 3 weeks, said it was the fuel pressure sensor, had road tested it and it was fine. I flew cross country to drive it home and after 30 miles at highway speed the same symptoms occured but the engine ran so I took it and am having it shipped home. We saw a pressure sensor recall but apparently this was not the problem. Any suggestions?

You are right. The engine, and dash, lost electrical power. This problem needs to be tackled as a (temporary) loss of electrical power. Any good mechanic, proficient in electrical troubleshooting, can handle this problem.