Thank you all for your replies!
MotownC: That was the device i was initially looking for. Great! But...
...when reading Zebra's reply i thought io myself why don't I just crimp(wording?) the cable myself. Since i only play PC or PS3 it doesn't really matter that only one is "live".
So what i did was simply buying usb plugs with open cable endings and connect them. Still don't know why such a cable isn't being sold anywhere. However....
Here is the result and it works perfectly with either PC and PS3 (Not both connected simultanously yet, but i guess that doesn't matter):