Fuel pump swap question

[FST4RD]

Not a Toyota, but probably the same. My '99 wrx needed a new fuel pump, got a DW200, came with a wiring loom that meant I could plug it straight to the standard plug. So I used it.
However the factory loom piece had this little black box plugged into the side, not in line and I don't know what it does or if it's needed. The car seems to run fine, but maybe someone could enlighten me.

[Grrrrrrr!]

Could be a noise suppression cap. Have you noticed any whine thru the stereo since you changed the pump?

[Stu-]

Yes thats what it is

[FST4RD]

Great. No I haven't thankfully.