No expert, but here my two cents..
1) The transformer. Transformers are rated to give a known AC secondary voltage at a known current. If your transformer is rated at 8 amps, it should deliver a secondary AC voltage of about 24 volts when it is asked for 8 amps AC. If it is asked for less AC current at the secondary winding, the AC voltage it delivers will be greater. Transformer manufacturers give a figure for "on load" and "off load" regulation. With a reasonably beefy transformer like yours, it might be (say) 7% to 10%. What that means is that if the transformer has a really light current demand, the secondary AC voltage might increase by as much as 10%. That puts the AC secondary voltage up to about 26.4 volts AC at no load, and should stay at the same 24v AC at 8 amps.
2) Bridge rectifier and capacitor.
Having passed through the bridge rectifier and capacitor, whatever the AC voltage is at the secondary output of the transformer, it will be transformed into a DC voltage which is
1.41 as large as the AC voltage
What this means is that 24v AC at the output of the transformer (working full stretch) will become about 33.8v DC. If however there is no load, the DC output will be 37v DC.
The value of the smoothing capacitors do not really affect the DC voltage (within reason). All they do is affect the ripple voltage about which the average DC voltage value flickers.
Sorry, there are whole websites that can explain this better... (had to try though..)