I can only assume you experienced a power surge but find it extremely difficult to explain why all the drives were fried,normally the psu would blow and possibly take out the motherboard but leave the drives intact...ok maybe the os drive could take a battering.
Did i get this right;
The psu was confirmed dead and replaced,then they say the psu was actually ok ?
If this is the case,i think you have been palmed off.
Others may have there own ideas.