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I have an old IRIS 4d/35 system with touchscreen capabilities and display
is CRT type.

Recently we upgraded the system to run on LCD displays where we needed to
provide the touchscreen controller with a separate power supply since the
power for the controller was previously drawn from the CRT power supply.

However when a new switching power supply was used the touchscreen did
not work. Reverting back to the supply from the CRT works flawlessly.

The supplies required for the touchscreen controller are 12V, -12V and
5V. The CRT power supply had a common ground and so does the new switching
power supply.

Any idea what could be the problem with the new power supply. Any advise
would be very much appreciated.

Does the touchscreen use a high "static" voltage (ultimately via the CRT
accelerating voltage) as part of its operation ?