Why Did My Power Cord Act Like a Fuse?

I don’t know enough about electricity to troubleshoot problems, so I’m looking for some answers.

All my electronics are fed AC through a pair of Porter Port outlets housed side-by-side in a single box. Each receptacle is on a dedicated line to a separate circuit breaker in the panel. This is all I could do to improve the wall wiring, because I live in a rented apartment. The apartment house was built in the early 70s, and the electrical panel is almost certainly original. My mono-block amps are plugged directly into the two receptacles of one of the Porter Port outlets. Plugged into the other outlet is my pre-amp and a good quality power strip to which my CD player and transport are connected. All power cords are good quality after market cords. The electronics are all solid state and left on all the time.

The other night when I came in from work, I put on a CD to play. The display panels of the CD player and pre-amp, which are clearly visible, were on and the digital readout on the CD player showed the disc was being read, but no sound. I then noticed that the small “power on” lights on the amps were off. Hmm. Flicking the on-off switches on the amps did nothing.

Another electrical circuit in the apartment sometimes cuts out for no apparent reason, which I can “fix” by flipping the circuit breaker off and on. So that’s what I decided to do for the circuit on which the amps were connected. When I flipped the circuit breaker back on, I heard a loud “pop” and quickly looking around the corner to the equipment rack saw a wisp of smoke. Ugh oh.

When I removed the amp power cords from the outlet, I saw that one cord had a neat little 1/4" hole on one side about three inches from the wall plug. I plugged the amps into the power strip, using a replacement for the damaged cord, and the system played. That was a relief. Later, when I went into my bedroom, the time display on my clock radio was flashing, indicating that the power to the entire apartment had gone off and come back on.

I contacted the electrician that wired the separate circuits for his thoughts on what happened. He thought the problem was a defective power cord, not the outlet or wiring. He suggested that I test the outlet where the problem occurred using a night light or cheap lamp, I did, and the lamp worked fine.

I have three questions.
First, when a circuit breaker is tripped, should equipment be turned off before the circuit is turned back on? If so, why? If there is a “surge” when the power is restored, why didn’t the power coming back on knock out any of my other audio equipment? I have flipped circuit breakers controlling lights on and off when the light switches are in the “on” position (to determine what fixtures were on which circuits), and the light bulb filaments (certainly more fragile than power cords) were not vaporized.

Second, it appears that the breaker on the amp circuit tripped while the other breakers did not. Is that because that breaker is defective or because the amps place greater current demands upon the electrical system than the other electronics? Incidently, my amps are each rated at 150 watt output, but the manufacturer does not provide specifications for power or current draw. They do have substantial toroidal transformers and run cool.

Third, even thought the lamp worked in the affected receptacle, could the problem possibly be with the wiring connections at the panel or the outlet but only become apparent when the amps are connected?

Fourth, is there any safe way I can test my damaged power cord to see if it still works? I plan to have it fixed, but I'm curious if only the insulation and jacket were affected or whether the conductor was fried.

Thanks for any answers to these questions and any ideas as to what went wrong.