In case of a blackout, the computer would turn off abruptly. When turned back on, the download manager should be able to pick up where it left off, as long as the server supports resuming interrupted downloads (most newer servers or those set up to handle a lot of downloads should support resuming).
In case of a brownout (temporary dip in power), the computer would likely reboot, after which the download manager might be able to automatically resume (if it has an option to start / resume downloads when the program starts, and it can be set to start with Windows).
It sounds like your recent blackout was preceded by a power surge, if damage was done. <img src="/ubbthreads/images/graemlins/cry.gif" alt="" /> A sudden drop or loss of power is not good for computers, but generally doesn't do physical damage. A half decent surge protector would help with power surges, though would not do anything to help with brownouts like a more expensive UPS would.
When I bought my first computer I lived in an older house, in an area susceptible to brownouts, and occasional 5 or 10 minute blackouts. After loosing a few email and documents in progress due to the computer suddenly rebooting (though the auto save feature of my email program and word processor helped with this), I decided to get a UPS. After I got the thing home and plugged in, it was a good 4 or 5 months before another brownout occurred. <img src="/ubbthreads/images/graemlins/suspicion.gif" alt="" />
