Big power resistors are expensive unless you use disposable light bulbs, then you can get advantage of the constant current characteristics when operating the bulbs in the 25% V rated range. This is due to the PTC non-linearity. Using fixed R's is dumb for cost and bulk reasons. Consider several series light bulbs (halogen) such that you have 25% of rated V on each lamp in series (3) dissipating 28W of waste heat to produce 6W of output at 48V. Low MTBF but it can work, but then 3 Halogen bulbs may cost more than buying a SMPS.
I use this method on occasions when I need a cheap and dirty power drop in the garden for DC power drop resistor for driving high power LEDs from a higher voltage on a long cable for convenience.
When cold, R tungsten is about 10% of R_hot=V^2/W . Warm will be a higher %, you can figure this out.
For 6 Watts at 48V you could drop 222V in a X-rated cap with 28VAR dissipation.
The impedance Zc(f)/Load ratio at line (Hz) may be estimated as a voltage divider but then for low ripple (10%) the load cap RC=T needs to be >8x line period thus limiting a C2/C1 (output/input ratio. THis "offline non-isolated" method requires a large primary plastic cap around 0.05 ~0.1uF which tends to be expensive rated for 600V and have MOV or Transil protection.
SMPS line regulators are superior in performance ( efficient, regulated andisolated) and lower cost when purchased, but DIY may cost more with the PCB design so buying is the best option for small qty.