This invention provides a design for the uninterruptible power supply system to make it more compact in size, more intelligent in handling primary power source and other power source failure, more efficient and reliable. This 600 to 1000 watt power system is capable of taking AC, DC and battery power inputs and distributes to multiple loads after conversion. Its power sentry monitors and controls all power inputs and outputs, and capable of switching power inputs without affecting the outputs in case of power source failure. The power sentry also controls the speeds of the cooling fans, charges the batteries, communicates with the operator, displays status, manages power consumption, prepares the substitute power source before switching power source, and shuts down the whole system incase of emergencies.