Need input designing a automatic backup power source using AC

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Joined Nov 10, 2019
Iam trying to design a circuit which has 2 AC(USA Mains) as Power sources a primary and secondary power source these sources can be on different legs or the same as each other it is possible a portable generator can be used as a power source aswell.Now i need the circuit to automatically switch from primary to secondary when the primary power source is disconnected,one other factor i need to consider is the device using the power sources shouldnt reset or loose power during the transition from primary to secondary source.

This might make the circuit either to complex or cost more but would still like to see if it would be possible,my first design consisted of using two simple SPST electromechanical one for Load and the other for Neutral i read the datasheet and the relay was saying it would have around a 5ms switch time, so i thought a high capacitance value capacitor that i put in parallel that would be used as the DC side power source would act as a power source for the 5ms switch time.The biggest problem i have is cost of the relays which the ones i found typically run around 11$ each for TO mount versions plus i havent figured a exact capacitor value to use but just looking at high uf capacitors there pretty high in price as well.I searched around and found Solid State Relays which have around 0.5ms switch time but from what i've found so far they can only be controlled from a low DC voltage.

Are the mechanical relays the only way to accomplish what iam trying to do?Is there any other IC's i can use?Any input or point in the right direction would be appreciated.Thanks
So I was trying to do something very similar with 12v and a battery backup Someone on the site sent me a link for an item that should work so here is the high voltage version
I believe us voltage is 110v in a residential propert? This allows 85 to 230 volts and 10a, it does say there is power loss of 1 second though.......

The simplest solution would be a ups but good quality ones can be pricey