This cable is kind a fascinating - it has an integrated boost converter, so you can plug it into any USB port (from a computer, battery pack, etc) and it will give you a higher DC voltage! It's a handy way to power 9V powered devices with a center-positive 2.1mm DC barrel jack from a USB port. We also have a version that provides 12V and if you just need a pass though cable, here's one for 5VDC.

These are rated at 500mA output, here's our measurements for various current draws when we set our bench supply to provide a steady 5V voltage

• 50 mA (9.0 V output), 100 mA,  90% efficiency
• 100 ma (8.95), 205 mA in, 87% efficiency
• 200 ma (8.9 V): 410 mA in, 86% efficiency
• 300 ma (8.8 V): 620 mA in, 85% efficiency
• 500 ma (8.8 V): 1060 mA in, 83% efficiency

So, overall there's a 90% efficiency at low current draw that drops do about 80% at high current use. There's also a 3 mA quiescent current. Note that often times the USB port voltage can droop too, and in addition you may have power losses with any thin or low quality cables with high resistivity!

Specifications:

• Cable Length: ~1.2 m / ~47"
• Weight: 35.1 g

Warranty: 30 days

• Warranty will not apply if Product fails or is damaged after delivery to you due to accident, abuse or misuse.

Package Includes:

• 1 x Adafruit 2777 USB to 2.1mm DC Booster Cable - 9V