Sounds like you need to get the fridge on its own separate fuse/circuit, or maybe a UPS (Uninterrupted Power Supply) A UPS can be a bit expensive but ones that have a short run life can include alarms that can be sent to a computer in the house to notify you, or maybe to a mobile device...Not sure what the newer versions do now...been awhile since I looked into them.
As for using any of the rats..if they all thawed through completely, to the point they are soft when squeezed, I would toss them. Even if they still feel cold, decomposition can occur pretty much in any temp above freeze though at a much slower rate. If they were warm to the touch, then they will be full of bacteria from decomposition. Some snakes may be able to handle carrion...but the gasses produced may cause problems...if not the bacteria itself, during digestion. Remember hearing about some people's snake that became suddenly very bloated to the point they pretty much exploded and died? I figured it was from food no digesting properly...either due to being too old rodents fed to them, or improper temperatures which allowed the meal to rat inside the snake, instead of digesting properly.
$500 is alot of money to have go down the drain, but better that than loosing valuable snakes.
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PHLdyPayne