Time Machine backups over wifi possible?

The 6-bay legacy units use an SFX form factor supply.  Most owners replacing them use the Seasonic SS-300SFD because it's an exact replacement except that the ATX connector cable is a bit too short and is also readilly available (in the USA) from Newegg.  It's the only one I've ever used, but I've looked at the specs for others who need to find a compatible supply in Europe (and now, Japan).  Silverstone and Corsair also make SFX form factor supplies.  On the other brands, the fan housing doesn't stick out like on the Silverstone, but the dimensions given on their web sites indicate they will fit.  They don't have the three 4-pin Molex connectors the NAS needs, but you can remove the connectors from the old supply and put them on the SATA conenctor wires (they just push in).  You will need an extender for the ATX connector on them, too, though I can't say if the 6" one that works with the Seasonic is right for them.  The specs for the Silverstone show the ATX cable is just a coule cm shorter than on the Seasonic.

The original is a 300W supply, with 3.3V @ 20A, +5V @ 20A, +12V1 @ 8A, +12V2 @ 14.5A, -12V @ .8A, and +5VSB @ 2A.  The 3.3V and 5V are probably delivering much more current than the NAS needs.  The 300W Silverstone supply is rated at slightly lower 3.3V and 5V currents, but more 12V and 5VSB.  And since start-up problems indicate that the 5VSB (SB is Standby -- the power that stay on all the time and controlls power on/off) is liikely your probelm and not only have I seen more of that kind of issue with the suplies here than others, that was also the problem with one of mine.  The Silverstone has only one 12V bus, but with plenty of current, so that shouldn't be a problem.  Their 450W supply has even more of each. 

BTW, if your Pro is an original Pro BE or Pioneer, then upgrading the processor can also help give it new life.  Compatible processors are quite inexpensive these days on eBay or directly from China.