You cant use Your Stand with the Dell Plate. The stands that work with the vesa plate go up and down and also rotate portrait and landscape with a swivel in the center held by 4 screws.
Vesa Plate Upgrade Required to mount a non-Dell Monitor to the flat panel stand (Kit)
VESA adapter plate For E-Flat Panel Monitor Stand
DP/N: Y009C KIT,PLT,MTG,VESA,E-FPM,75/100M
DP/N: G999H. CUS, PLT, MTG, VESA, E-FPM
So the G999H , Y009C is compatible with the following but not limited to:
Dell E-Series Flat Panel Monitor Stand DELL 330-0874, R427C, RM361, T545C, M520M E-FPM Monitor Stand and Laptop Notebook Dock For Dell Latitude E4200, E4300, E5400, E5500, E6400 / 6400ATG, E6500 E-Family Laptops and Precision M2400, M4400, M6400 Mobile
So you remove the Dell Plate with fingers by removing the 4 screws in the center and put this plate on. Then you put the standard screws for vesa mounting thru the plate via the rear.
That needs a stand with mounting like this.