rebel wrote:
Based on experience I'd still lean towards the mobo being the problem, but doing
the PSU test certainly will identify the problem area.

Hope so :-)

Doing a little research, the extra pin connector is for a Dallas 1-Wire
serial id chip that Dell have built into their own manufactured power
supplies, to limit their customers to only purchasing them and not a
compatible.

If it is the PSU at fault, further googling suggests that replacement
supplies from Dell are actually not that horrendously expensive (e.g.
£33 inc delivery for UK)

--
Adrian C