When we buy new device such as APC 990-4053 we often through away most of the documentation but the warranty.
Very often issues with APC 990-4053 begin only after the warranty period ends and you may want to find how to repair it or just do some service work.
Even oftener it is hard to remember what does each function in Power Supply APC 990-4053 is responsible for and what options to choose for expected result.
Fortunately you can find all manuals for Power Supply on our side using links below.