While the whole electric system is a mess yet... one of the most noticeable one even with normal operation is when BUS OFF light are shown (eg. one engine shutdown, or turn one GEN switch to off). EFIS on that side would black out.
As per FCOM v2 10.40 EFIS system Description, Electrical Power, EFIS is powered by 115v AC power BUS, which is connected to AC TRANSFER BUS. The Transfer bus can get power automatically from opposite generator bus,so EFIS would only loss power with loss of ALL airplane generators (and no GPU).
The TRANSFER BUS light above BUS OFF light are functioning mostly correct, so for simplification, as long as one side's TRANSFER BUS light are off (of course not because no BAT power), the related EFIS should be able to show.