A separate power supply may be needed. Retailers satisfy demand identified through a supply chain. First the device can supply too much power. The exchange rates between the metals varied with supply and demand. This eliminates the need for a separate power supply from some devices. They usually recharge with a USB power supply. The British had both supply side and demand side advantages. It has an external 85W power supply . Consider an example of linear supply and demand curves. Rod Holt developed the unique power supply. The level of access to water supply and sanitation has been increased significantly. A railgun requires a pulsed DC power supply. Access to improved water supply and sanitation in the UK is universal. This was due to shortages in fuel supply. Marshall explained price by the intersection of supply and demand curves.