if you have a ups does it have to be rated at the psu rating ex. if you have a 750 watt psu do you need a 750 watt ups or can you go higher or lower for the ups

not sure of this from a hands on from point of view but from a purely engineering perspective you have 2 ways to think on this

1. does my UPS provide enough watts to provide for a power outage

2. how long will it last for?

For point 1, look at the sustainable power output of you UPS vs the requirements of your system (both in Watts, without knowing your system i have no idea what the value is)

For point number two you have to look at the Watts/hours rating and be aware their interchangeable, i'e 1000W/hr would mean it can supply for 1000W for one hour....or 1W for 1000 hours...or anything inbetween

To conclude, choose a UPS that can meet the maximum drain of your system in terms of watts and then choose how long you think you need the backup to last for

Hope thats helps,

Carod

Side note....make sure it is sustainable power output...many PSU companies quote ampage/power ratings in term of short burst, without going into details which i can't be arsed to do just take this to be a bollox figure, it means little, a bit like PMPO ratings on music amps instead of rms values

thanks for the info

no worries, i'vd been told i'm a good engineer but a crap teacher