Ultra / Super Isolation Transformers are effective for Isolating sensitive equipment's from Line Voltage transients, spikes & DC Leakage etc. They are specially designed forsensitive critical equipments like computers & peripherals, medical instrumentation, digital communication telemetry systems, CNC Machines etc. and stopping such disturbances generated by the noisy equipment load from being injected into the power line. Multiple shielding techniques employed reduce the inter winding capacitance to below 0.005 Pico farad and increases DC Isolation to over 1000 Megaohms.
Technically, any transformers that have no direct current path between it's primary & secondary windings provides Isolation. Other commonly used, transformers even if they have separate primary & secondary winding are intended to convert the input voltage to a more useful level & do very little to attenuate the passage of noise or transients from primary to secondary. Even though both are separately wound transformers, they are substantially different w.r.t. Construction, specification & performance characteristics.