VGA cable

At present I have a Dell vga cable fitted to my inspiron 580 desktop...I wanted to move my monitor to a different place on my work station..which requires a longer cable to be fitted.,..I have tried several longer  new VGA cables, but each one affects my graphics (causes everything to appear stretched). On looking at the original cable, there appears to be some sort of "supressor" on the cable and and the only ones I can find in the shops do not have it. So I am assuming that is what is causing the problem. Can you advise if Dell sell a longer VGA cable with this " supressor "or can these be bought anywhere and if so what do I ask for ?