We start with the original "International Power Sources, Inc. Nortel HUP80"
triple-output power supply.
Cut and remove DIN connector and outer RFI clamp.
Strip off a couple of inches of the outer black insulation.
Attach crimp pins to each of the 6 colored wires.
Leave bare grounding wire for later use.
See close-up of crimp pins (be careful of stray whiskers).
Please check the voltages before you attach the Thunderbolt DC connector:
BROWN (-12), WHITE=BLUE (common), RED (+12), YELLOW=BLACK (+5), bare wire (mains ground).
It is possible your power supply uses different colors.
Detail of DC connector.
Final result (some people ground the frame, some don't).