Even at the default TDP of 38.5w (4 cards @ 154w), that's still dangerously close to the limit. Try to connect as few cards as possible to each power lead, or use a higher rated connector designed for more power, like the 6-pin or 8-pin PEG connectors.
I don't get why some are voluntarily going from 38.5 W to 65 W for maybe 10-15% higher kHash/s rates.
This kills Maxwells excellent power efficiency.... and apparently also PSU cable connectors.
Christian