This bug is basically Devices/Power source (item) that can be multiplied due to some bug I don't know.
Step 1: Collect materials for your item.
Step 2: Prepare a worthless block/your old Device.
Step 3: Arrange your materials on the Assembler to create your item.
Step 4: Make your item and then make it replace your block/old Device.
Step 5: You will notice that the materials for your item is still intact.
Step 6: All done! You can keep on making items until you do not have any more blocks/Devices.
Please feel free to change formatting of this useful bug.
The bug was tested on version 1.91. This bug may be fixed in a future update.(unlikely)