It is quite possible. Trying to draw more power than a PSU is able to provide can lead to expensive consequences. The PSU itself is likely to have been damaged and, if the regulators within have been damaged, there is a distinct possibility of other hardware failure. Of course, it is quite possible that there has been no damage to the hardware apart from the PSU (you can check this by replacing with a known good unit of sufficient capacity), but given the margin of the excess power drawn on the 250W unit, I wouldn't hold my breath. In addition, the 550ti card requires a 6-pin power connection to the card itself, and a 250W PSU is almost certainly not going to feature such a connector. In that case, the card will try to draw the power through the slot, and potentially cause damage by trying to draw more power along the motherboard tracks than they were designed for (can lead to track burnout).
Sorry to be the bearer of bad news, but consider it an expensive lesson learned.