Ultra / Super Isolation Transformers are effective for Isolating sensitive equipment from Line Voltage transients & DC Voltage leakage etc. They arc specially designed for sensitive critical equipment's 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 Mega ohms.
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 alternate the passage of noise or transients from primary to secondary.