The answer for your question is ‘no’.

You’re never going to reduce power usage substantially by swapping PSUs, because there’s just not enough efficiency gains to be had even if a Pico PSU was more efficient which they really aren’t.

You say the hardware is ‘nothing too different’ but you mention ddr4 vs 3, which makes me think the Dell is a generation or few older which could easily impact power draw by 10w.