I have an old scanner, HP Scanjet 3400C, but I have lost the power supply cable. The power socket the cable fits into looks like a small single hole with a little pin in the middle.Can I replace it and what is it called?Thank you very much.
The power cable and adapter will probably be unique to the scanner. You'll have to order the right one from HP, or through a computer store. The USB cable should be standard. Most printers and scanners use a USB cable with a Type A connector (flat) on one end, and a Type B connector (squared-off) on the other end. They're easy to find at Staples, as well as at computer stores.
