I have a string of 30 3mm LEDs attached to a battery pack which holds 3 C-size cells and has a switch, and a 10ohm 10% resistor (brown black black silver). I'm not sure of the exact specs for the individual LEDs, but they look pretty standard (warm-white, 3mm.) I think they are connected in parallel (2 wires in to each, 2 wires out) I also have a power block (wall wart) from an old vacuum which outputs 5V DC 140Ma. Is it possible to power the LED string with the power block, and if so, what kind or resistor should I substitute for the original? (and, for future reference, how did you arrive at your answer?) How does supply wattage matter? Might as well throw this in as well: what resistor would I need to power them with USB?