Electrical – Remove power spike when restoring power

Neither device is probably pulling the rated amount, though it might hit those ratings at peak. If you started the vacuum and saw at the exact same time, you might trip the breaker.

Assuming the breaker isn't defective, if it hasn't tripped you're OK from a capacity point of view. Keep in mind there might be other devices on the circuit too.

Ideally you wouldn't use an extension cord at all for this. While you probably won't run into any problems, you might consider a heavier wire gauge for the extension cord. If you don't need all 50', you're also better off with a shorter extension cord.

The "four rooms on a breaker" and the re-trip with a flash, along with the routine shutoffs owing to rewiring the poles... together completes the picture.

Four rooms is an enormous load for any circuit, especially when one of them is a kitchen. And this is a smaller 15A circuit. And there are "safety power strips"** and as such, I suspect there are also other loads which you did not mention or are unaware of.

In any case, this circuit is certainly maxed out.

It's also possible the fridge is getting old and tired, or even having a ground fault.

So here's what we know. When you reclosed the breaker, you got a flash, "foof" and retrip. And you did it again (bad move), same result.

Certainly it's reasonable to assume that if you manually shut it off, and later turned it back on, it would trip again. Ditto if you shut off the whole panel/house. Ditto if there was a power outage, and not all outages have to do with scheduled work. (This assumes the freezer has warmed up a bit and wants to cycle on: if the freezer is sanguine, it may not trip.)

This is an immediate, big-flash, magnetic mode trip, which only happens at 5 to 10 times a breaker's thermal mode current rating. What would cause that? Inrush current at startup - this is a characteristic of most motors, most lightbulbs, and most power supplies. And this explains why you can power everything up if you start each one at a time. The fridge's current draw is dramatically lower once its motor has spun up, so as long as you introduce each inrush current one at a time, you are OK.

Inrush current is why the breaker's magnetic trip rating is so much higher than its thermal trip rating. A great deal of it is tolerated.

On power restore, everything restarts at once and they are stacking to cause a magnetic trip. This shouldn't happen. Either one appliance is defective and causing an extraordinary startup load, or you just have way too much stuff on this circuit.

Inrush current applies every time an appliance cycles on, e.g. A fridge will turn on and off intermittently as needed. If two big appliances both happen to cycle at the same time, you will get a spurious, unexplained trip.

What you really need is a dedicated circuit for fridge and for freezer. If the landlord is fond of removing the panel deadface, this shouldn't be too much of a challenge for him, I see 3 empty spaces.

Or it may be time to replace an old fridge, or at least its motor's start capacitor.

Figure out which loads are on which breakers, and how much each load realistically draws... and move things around so they are sane. A Kill-a-Watt will tell you what any appliance or power strip draws. Unfortunately I don't onow of a device like that which will tell you about inrush current.

** "safety power strips" are not a thing, by the way. Strips are receptacle splitters, to give you 6 sockets where you had 2. Used well, they can be safe, but all the loads on them together add to the demand on the circuit, so it is exactly the same as if they were plugged in directly. So if the notion is "they let me plug more stuff in", that is only true if all their power draws add up to a sensible number.

As far as safety, they certainly add anything but that, and they are probably the cheapest and most shoddily made part of your entire wiring system (unless they're Tripp-Lite, then nevermind.) Perhaps they mean "as opposed to this other unsafe power strip".