Yes the problem i when the electricity is interrupted...and i need some minutes to turn everything off.
But anyway i would like to understand if there are some side effects in plugging the rme 802 to an ups....like noises hums or so.

There are different types of UPS - the most expensive are what are called "on-line" and provide battery power all the time, while simultaneously charging the battery when connected to AC power. There is usually a goodly amount of filtering applied to the output of these devices, such that the power they provide is very close to a smooth sine wave. Some of the costlier Tripp-lite UPS devices are like this.

Most of the other kinds, like those you find in office supply stores and the like, are "off-line" and only draw on the battery when the AC fails, so in the event of a power failure, there will be a brief period between the stoppage of the AC, and when the battery takes over. This can result in power spikes which can affect phantom power supply and might be damaging to any circuits providing high gain, such as pre-amps for ribbon microphones.

Further cost cutting measures in the cheaper UPS devices include reducing the amount of AC filtering applied to the power provided. Instead of a smooth sine wave, it will be more like a square wave, with all the buzzy harmonics, which can pollute your audio chain, including microphone pre-amp signals. The leakage might be so strong that some damage might occur, but even at best, it's not going to be something that you'll want to record.

It's possible that in the event of a power failure, all this will happen far too quickly for you to take any steps to protect your gear, so unless you get a UPS of sufficient quality that it provides a smooth change-over from one power source to the other (or no change-over, as would be the case with an "on-line" UPS), it's possible that what you DO spend for protection will wind up providing little to none. I'd recommend that you do a good amount of research before making a purchase.