I'm building my first PC and can't seem to find the USB power cable (the one that is meant to connect to JUSB1 on the motherboard). Is this normal? I can't even find where the cable should be coming from, should it be coming from the Powersupply or the pc case?
There are no internal "USB power cables." Motherboards have USB headers to attach USB ports (usually on the front of the case) and their power comes from the motherboard's own power rails.
If your case has no USB 2.0 cables, leave those headers alone unless you need the ports they provide access to. Certainly do not attempt to plug a power cable into those headers, as this will damage the system.
Oh I see, I may have seen the issue. The case is the Corsair 100R and the motherboard is the MSI B450 Gaming Plus. I think I just have the USB 3 Power cable to connect to the motherboard, no USB 2. Can anyone confirm this?