The current PSU is 530W and is only connected in 4 places, the HDD, the CPU, The 24PIN and the 6pin for the GPU. Nothing at all looks full of dust since its not even 3 months old.
That's what the label says but, from memory Raidmax don't state the combined 12V output max
There's absolutely no chance I'd expect that unit to do >300W reliably, if that.
I think it's safe to say it's the board, or the PSU. Not saying it can't be anything else but, given the relative quality of your system specs otherwise, the PSU strikes me as the most logical culprit.
An interesting note - that PSU has been around since ~2013. It took until 2017 to have it tested for 80+ compliance. Not that efficiency is the be-all, end-all, but interesting none the less.
https://www.plugloadsolutions.com/80PlusPowerSuppliesDetail.aspx?id=104&type=2
But isnt it true that PSU's operate most effectively at about 50-80% power draw?
Not effectively, efficiently. And yes, as per 80+ spec, a PSU will be most efficient at 50% of it's rated capacity.
The thing is, between a 1600X (95W) and a 1050 (75W), those numbers are so low that #1 efficiency is almost a moot point & #2, peak efficiency (50%) would only really be obtained on a ~350W PSU, of which there are very few viable options.
Why does the computer then boot for a few seconds when i leave it off for an entire night?
That, I'm not sure about. A pure guess here, but perhaps it;s discharging the residual power from the capacitors overnight & you're truly starting from an outright 'cold' boot in the morning. I'm not sure though.