ALTDEV ALT EXCURSION OVERSHOT.

Narrative

PREFLT AND THE BEFORE STARTING ENGS CHKLIST; PWR WAS ACCIDENTALLY REMOVED FROM ACFT BEFORE APU GENERATOR CAME ON LINE. THIS CAUSED A 10 SECOND (APPROX) LOS OF ACFT PWR WHICH DUMPED MOST FMC AND ACARS DATA WHICH HAD BEEN LOADED. WE THEN RELOADED AND RECHKED ALL FMC INPUTS; CAUSING A 10 MIN DEP DELAY. ON TAXI OUT WE COMPLETED THE REMAINING CHKLISTS; BUT FAILED TO NOTICE THAT THE PWR LOSS HAD CHANGED THE TKOF ALT ON THE AFDS PANEL. THE PWR LOSS CHANGED OUR ALT ON THE AFDS PANEL FROM THE PREVIOUSLY SET 5000 FT TO 10000 FT. WHEN DOING CHKLIST I CALLED FOR THE CHKLIST ITEM AFDS PANEL ON THE BEFORE TKOF CHKLIST. THE CAPT READ OFF WHAT WAS IN AFDS WINDOWS V2 OR 135/RWY HDG OF 090/AND ALT 10000 AND EVERYTHING SEEMED TO REGISTER AS CORRECT; BUT PART OF MY CONCENTRATION WAS DISTR BY DUMPED ACARS DATA. I WAS ATTEMPTING TO RELOAD; RADIO CALLS; CLRING FOR TAXIING ACFT ON A VERY BUSY NIGHT. SHORTLY THEREAFTER WE WERE CLRED FOR TKOF. I WAS FLYING THE LEG AND I NOTICED THE CAPT CALLED DEP ABOUT 4 TIMES WITH NO LUCK IN GETTING THROUGH. WHEN HE FINALLY GOT THROUGH I WAS FLYING THROUGH 6000 FOR 10000 WHEN THE CTLR ASKED WHAT WE WERE DOING. THE CAPT REPLIED THAT 10000 WAS OUR CLRED ALT. I FEEL THAT THIS PROBLEM WAS CAUSED BY THE PWR LOSS WHICH CHANGED THE ALT FROM 5000 TO 10000 ON THE AFDS PANEL AND DISTRS CAUSED BY THE INCREASED WORKLOAD GENERATED BY RELOADING AND RECHKING ALL FMC AND ACARS DATA AFTER DEP TIME AND DURING TAXI OUT. SUPPLEMENTAL INFO FROM ACN 204942. WHEN DOING AFDS PANEL CHK I CALLED OUT ALT 10000 FT BUT THIS DID NOT REGISTER AS INCORRECT AS I ASSUMED COPLT HAD RESET NEW ALT. THE ERROR; IN MY OPINION; WAS GENERATED BY THE ALT SHIFT FROM 5000 TO 10000 CAUSED BY THE ELECTRIC PWR SHIFT AND OUR DISTR CAUSED BY THE INCREASED WORKLOAD AND BEING UNABLE TO CONTACT DEP CTL IMMEDIATELY.