A cable apparatus comprising: a cable (410, 510, 610, 710, 810, 910); a first plug (420, 520, 620, 720, 820, 920) coupled to a first end of the cable (410, 510, 610, 710, 810, 910) and a second plug (450, 550, 650, 750, 850, 950) coupled to a second end of the cable (410, 510, 610, 710, 810, 910); characterised in that the first plug (420, 520, 620, 720, 820, 920) comprises: a first active circuit to receive and retime data, and to provide the retimed data; and a first circuit to receive a first supply voltage from a first device (480, 580, 680, 780, 880, 980) connected at the first plug (420, 520, 620, 720, 820, 920) and to determine if the first supply voltage is above a threshold voltage; and the second plug (450, 550, 650, 750, 850, 950) comprises: a second active circuit to receive and retime data, and to provide the retimed data; and a second circuit, wherein if the first supply voltage is below the first threshold, then the first circuit powers the first active circuit with the first supply voltage and provides a second power supply to the second circuit, and the second circuit powers the second active circuit with the second power supply, and if the first supply voltage is not below the first threshold, the first circuit and the second circuit each receive a third supply voltage generated from the first supply voltage in a second device (490, 590, 690, 790, 890, 990) connected at the second plug (450, 550, 650, 750, 850, 950), and the first circuit powers the first active circuit with the third supply voltage, and the second circuit powers the second active circuit with the third supply voltage. a cable (410, 510, 610, 710, 810, 910); a first plug (420, 520, 620, 720, 820, 920) coupled to a first end of the cable (410, 510, 610, 710, 810, 910) and a second plug (450, 550, 650, 750, 850, 950) coupled to a second end of the cable (410, 510, 610, 710, 810, 910); characterised in that the first plug (420, 520, 620, 720, 820, 920) comprises: a first active circuit to receive and retime data, and to provide the retimed data; and a first circuit to receive a first supply voltage from a first device (480, 580, 680, 780, 880, 980) connected at the first plug (420, 520, 620, 720, 820, 920) and to determine if the first supply voltage is above a threshold voltage; and the second plug (450, 550, 650, 750, 850, 950) comprises: a second active circuit to receive and retime data, and to provide the retimed data; and a second circuit, wherein if the first supply voltage is below the first threshold, then the first circuit powers the first active circuit with the first supply voltage and provides a second power supply to the second circuit, and the second circuit powers the second active circuit with the second power supply, and if the first supply voltage is not below the first threshold, the first circuit and the second circuit each receive a third supply voltage generated from the first supply voltage in a second device (490, 590, 690, 790, 890, 990) connected at the second plug (450, 550, 650, 750, 850, 950), and the first circuit powers the first active circuit with the third supply voltage, and the second circuit powers the second active circuit with the third supply voltage. a first active circuit to receive and retime data, and to provide the retimed data; and a first circuit to receive a first supply voltage from a first device (480, 580, 680, 780, 880, 980) connected at the first plug (420, 520, 620, 720, 820, 920) and to determine if the first supply voltage is above a threshold voltage; and the second plug (450, 550, 650, 750, 850, 950) comprises: a second active circuit to receive and retime data, and to provide the retimed data; and a second circuit, wherein if the first supply voltage is below the first threshold, then the first circuit powers the first active circuit with the first supply voltage and provides a second power supply to the second circuit, and the second circuit powers the second active circuit with the second power supply, and if the first supply voltage is not below the first threshold, the first circuit and the second circuit each receive a third supply voltage generated from the first supply voltage in a second device (490, 590, 690, 790, 890, 990) connected at the second plug (450, 550, 650, 750, 850, 950), and the first circuit powers the first active circuit with the third supply voltage, and the second circuit powers the second active circuit with the third supply voltage. a second active circuit to receive and retime data, and to provide the retimed data; and a second circuit, wherein if the first supply voltage is below the first threshold, then the first circuit powers the first active circuit with the first supply voltage and provides a second power supply to the second circuit, and the second circuit powers the second active circuit with the second power supply, and if the first supply voltage is not below the first threshold, the first circuit and the second circuit each receive a third supply voltage generated from the first supply voltage in a second device (490, 590, 690, 790, 890, 990) connected at the second plug (450, 550, 650, 750, 850, 950), and the first circuit powers the first active circuit with the third supply voltage, and the second circuit powers the second active circuit with the third supply voltage.