The trimmer potentiometer in power supplies is usually marked with V adj (voltage adjusment) symbol and in one Aliexpress picture of this power supply, it would be near the edge of the PSU connector row closest to the Simucube motherboard. It is a small knob that can be turned with a Phillips screwdriver.
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thank you Mika, appreciate it, will try it tomorrow in day light and update you and share outcome 
can’t thank you enough for your help and support Mika.
hi Mika, so took the risk and tested around and did the voltage adjustment, SO FAR SO GOOD! 
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update here, been having FFB cut outs randomly, for days and weeks smooth sailing, then few on and off days, in iRacing the FFB just randomly cuts out. could this or would this be a PSU issue? maybe help to replace the PSU inside the controller box?
maybe best to replace the old GYU PSU with a MEANWELL SE-600-48? would this meanwell be the right fit? https://www.meanwell.com/productPdf.aspx?i=469
or maybe replace GSYSPW with Meanwell SDR-960-48 https://www.meanwell-web.com/en-gb/ac-dc-industrial-din-rail-power-supply-output-sdr--960--48 ?
at least the SDR is a good choice, if you are in 250 V AC mains voltage country.
yes in 250V AC region.