as a DIT frustrated with the often reliance on the spark's generator schedule i'm draw to the idea of getting one of these. has anyone any advice/recommendations for brands/models? processes power and electrical i find quite confusing so an idiots guide would be muchly appreciated!
Do you mean you want to buy a generator, or a UPS?
I was a little confused by the post, but I'm assuming UPS since that is whats in the subject line.
For a UPS it's really about how big a load you have, and how long do you need it to run.
If the UPS rating is in Watts, and your gear is probably in Amps, just remember that Watts=Volts x Amps. For example, a piece of gear that is 120V, and draws 8A is using 960W.
For comparison, a typical 120V circuit in a commercial building can continuously supply around 2000W before tripping a breaker. A home 15A circuit about 200W less than that.
Also note that a lot of quoted UPS capacities are input consumption, not output, be sure to read the fine print.
First, add up all the gear you want to protect, and get a UPS that is at least 25-50% more than that. Keep in mind, not everything needs to be on the UPS if your budget is tight. Once the load gets over 50% of the UPS total, the reliability and the run time takes a nose dive. Also when the batteries start to age, you will loose some run time, and when most of the bigger UPS' are running they have a cooling fan taking some of the juice, so it's good to have some headroom.
Second, you need to look at how long you want to run the gear, and then 'up size' the UPS to meet that goal.
Since we don't know how much gear your trying to protect, or what your budget is, it's hard to take a guess at cost. Once you get into really big units, the cost per watt can be quite high, since they are not mass produced in the quantities that a typical large office unit of a 1000w or so.
Unless you have a really small load, or a lot of cash, you'll find that your mostly looking at enough run time to get the gear shut down properly, with a couple of minutes to spare.
May I also suggest looking at a power conditioner in-line before your UPS.
When running off a generator, be it a genny trailer on a feature or the simple genny from a small production motor home, my biggest issue has been the fluctuation in voltage causes the UPS to constantly switch from line to battery power. Not only does this cause the warning beep to go like crazy but it drains the battery to the point that it's useless if a cut-off were to actually happen.
A good conditioner is a few hundred ($100-300) and you'll find them mostly advertised to the studio audio/high end home audio world.