Hi I couldn't tell you the model number, but I think you will find it is the bigger one of the two types that emu fitted on the ultras. This larger psu was used because the e4xt and platinum both have more optional boards fitted and so require more juice.
I have the platinum and in December it had a power problem similar to yours (drive spinning, display lighting but no information and no fan) I sent the rack to Cyberwave who are a synth repair specialists. The engineers name is Ben and he told me that one of the rails on the psu was down. He got the unit running sweet and returned it. I was delighted with the service and can highly recommend him.
Check out the Cyberwave website here for more info......
http://www.vintagesynths.co.uk/