How to tell the current from the amp

I get the case where you have double the wattage with half the impedance, but such case only show the device is qualified as high current, but now by how high as a quantifiable measurement. It’s only a relative measurement. So there is no one measurement available to indicate the “current” capability? I don’t have electrical technical back, and I feel this concept is being mystified…

Measure the voltage.
The equation V=IR can be refactored to be I = V/R.

Once you have V and the impedance plot, then you know R at any, and all, frequencies.

If it is a constant 8 ohms, then I=V/8.
If it is 2 ohms, the I=V/2
If it varies with frequency, then it gets harder.

There is not a lot more to it than ^that^.

If the amp it trying to hit 50V, but only have rails at 28V, then you run out of voltage.
If the impedance that you are trying to drive is low, and the power supply has little capacitance and undersized in the transformer, then you cannot maintain the “umph” for very long.

If you are concerned with current, then you likely have a speaker than is very low impedance, or maybe have been told that you should be looking for current specs as a way to determine which amp to use.

I will just add that amplifiers with FET's typically have a higher current rating than bi-polar devices. This also yields to a high slew-rate which helps with transient peaks. I've not seen tube amplifiers that can match current capabilities of SS FET amplifiers.

Been running ESLs since the '70's with 55, 60, 70, 100, 140 and 200 watts.

Sorry bub, never "a problem."

:(-

Most amps in the “Hi-Fi” realm have info associated with them discussing current, watts etc. Unless you are trying to drive very inefficient speakers and/or a speaker that dips into painful loads under 2 ohms, and listen very loud, it’s not a problem. The knowledge of the doubling down factor of watts/ohms is something that is known and easy to find out. If an amp doubles down from 100/8 to 200/4 but craps out down to 2, then you know the amp will struggle if put into a hard to drive speaker. This info is often listed, or a quick phone call to ascertain if the amp is stable at two ohms gets the job done.

I was thinking of trying Peachtree’s new 1000w GAN digital amp. But their power rating numbers didn’t look great past 4ohms. I called them and they recommended I not use it as it wasn’t really a good mix for 2ohm loads, which is fairly typical of digital amps. Other than those factors, the actual current doesn’t really matter much. You just need to be sure to get an appropriate amp for the speakers you intend to use.

Thank you all for the comprehensive science lesson. Really learned a lot here. I guess my point is the "lineality" (not sure if the right word) of co-relation between volts and impedance can be measured, and should be clearly marketed when a consumer is looking for a "current capable" amplifier, rather than using indirect formula to figure it out by themselves. 100/8 and 200/4 is just an indirect measurement, and i am sure there are ones perform 100/8 and 180/4, or more, or less.  Why not just use one measurement to tell clearly, instead of leaving the consumer scratching the head and guestimate the math himself.