Look for a zener diode, probably on the output of the B+ R/C filter chain. Actually, there are commonly two zeners in series. If it's Chinese, they're usually silver in color and connect just before the jumper that feeds the pattern select switch. If you find such, lift the negative end (right by the output) and measure the resulting voltage increase. Your B+ will now be unregulated, but you should see more voltage available at the PS output. In my world, I set the dropping resistors so that the B+ delivered to the mic is what I want. Then, I put a zener across the output of the supply that is 10V higher than the B+ value I want the mic to see. The zener only conducts when there is low or no current being drawn. Almost always, that's when someone has turned on the supply when there's no mic plugged into it. With no mic plugged in and no "safety zener", the B+ will go all the way up to the voltage level exiting the rectifier. Not a good thing for several reasons. Again, this "safety zener" only conducts when it's protecting your circuitry, so no zener noise is added inside your PS during normal operation. If you're using a supply with a high voltage regulator, that's a different story, but most of the Chinese supplies only have a single zener (or two in series) as B+ regulation.
And, relative to Abby Road D Enfur's comment about the mains, make sure - if it has a switch - that it is set for the proper mains voltage.
By the way, you don't need a 630V output cap. You can save some space in your mic and some money for future builds....
