As usual, Sean's comments are correct. You must choose a device that is capable of delivering the current that your components require.
There are some other considerations. A normal transformer is not a voltage regulator. If the input goes up or down, the output follows along. If the device your dealer is selling does indeed maintain a constant output voltage then it is more complex than just a transformer.
As for building your own, that is relatively simple IF you know what you are doing. You are dealing with line voltage here and an improperly designed conditioner could easily be a fire and/or an electrical shock hazard.
One of the big advantage of some of these isolation devices is that they convert your AC from unbalanced to balanced. This can potentially greatly reduce the amount of noise and hum in your system.
A transformer is also not an ideal isolation device. If it were then you would not need an extra one since every amp, preamp, etc. that you have already has a transformer in it. Since a transformer does not completely isolate your components, they usually contain contain surge suppressors and noise filters so getting a box and a transformer would not be the same as buying one of these units. Devices such as the MIT ISO have filters to keep noise from entering or leaving.
As with all things in this hobby, the only way to tell if a particular device will benefit your system is to try it.
There are some other considerations. A normal transformer is not a voltage regulator. If the input goes up or down, the output follows along. If the device your dealer is selling does indeed maintain a constant output voltage then it is more complex than just a transformer.
As for building your own, that is relatively simple IF you know what you are doing. You are dealing with line voltage here and an improperly designed conditioner could easily be a fire and/or an electrical shock hazard.
One of the big advantage of some of these isolation devices is that they convert your AC from unbalanced to balanced. This can potentially greatly reduce the amount of noise and hum in your system.
A transformer is also not an ideal isolation device. If it were then you would not need an extra one since every amp, preamp, etc. that you have already has a transformer in it. Since a transformer does not completely isolate your components, they usually contain contain surge suppressors and noise filters so getting a box and a transformer would not be the same as buying one of these units. Devices such as the MIT ISO have filters to keep noise from entering or leaving.
As with all things in this hobby, the only way to tell if a particular device will benefit your system is to try it.