uhhh, no. A single drive does not require more power than the power supply should output. If your system can't handle it, then you have a faulty power supply. It even has enough power to power up 2 750gb drives, the most power draw out of all the models of drives.
What you are doing can cause severe and irreversible damage to your drive and or tivo. The power supply in the tivo, if you notice, has a power connector running to the motherboard for a reason. Yes, you may have solved your drive spinning up, but you still haven't solved the fact that your tivo's power supply has something wrong with it. I wouldn't be shocked to hear down the road that your motherboard burns up.