I got the replacement power supply from my distributor and it solved the problem. The only obstacle was that I had to remove the motherboard to replace the power supply - not the best of solutions. It should be an easy fix for Antec to build the left side of the tower so that it is possible to slide the power amp out without having to rebuild the entire computer.
I ran the scimark2 benchmark again.
Composite Score: 271.17860249249054 FFT (1024): 109.01504 SOR (100x100): 509.6416128038548 Monte Carlo : 41.09544600963967 Sparse matmult (N=1000, nz=5000): 241.0298025378471 LU (100x100): 455.1111111111111 java.vendor: Sun Microsystems Inc. java.version: 1.5.0_06 os.arch: x86 os.name: Windows XP os.version: 5.1
So, the new machine is 1.7 times faster than the previous score.