Purchase of a Cheap UPS: Comparing Ever Eco 500VA & ElSist 1800VA for 30min Backup at 35-40W Load

Hello everyone after a long break of absence from the forum,
if the thread started in the wrong topic, please move it.
Recently, in my apartment in the block there is a power failure - power outage for some time - unfortunately just in the hours when a man is getting ready for work. Soon it will be dark during these hours, which is why I need to buy a cheap uninterruptible power supply quickly. Fast for temporary work, because I am now quite often in trips and I had to stop my work on a slightly better system based on 12v buffer power supply and microcontroller, and such a UPS would simply be plug and play, which the other half would not have to complain about, that in the morning he can't do makeup for work in the dark.
I need to have a backup time of about 30 minutes at a load of 35 - 40 watts.
I found:
http://allegro.pl/ups-ever-eco-500va-300wat-nowe-baterie-fvat-321-i6945681166.html
http://allegro.pl/nowy-ups-elsist-1800va-400w-7ah-gwarancja-fv-23-i6926755588.html

I am asking for advice, they may of course be different but in a similar price range.
As I mentioned, UPS is cheap, because it is only a temporary solution, the target will be better and more efficient, here the voltage will be boosted once to 230, then lowered to led bulbs so performance is out of the question, but I need some time to finish my "device" which I don't have much because of my trips. I need to make it up to a few months, if it lasts longer and does not break, I will use it for something,
The devices it has to support the clock radio and bulb (or 2) led with a total power (all) 35-40 watt, so you do not need full sine, it is enough to modify or rectangular course.
I am asking for suggestion.
greetings

Do you have separate circuits e.g. in the bathroom / bedroom to which you connect this UPS? Contrary to appearances, the clock radio may not cope with the rectangle, most are synchronized with the network.

A separate circuit will be a strip connected to the UPS to which the floor lamp and the clock radio will be connected.
I don't really see the electrical justification for the clock radio not working. Can you tell why more? Out of curiosity, I connected it to a car inverter (a straight one with a rectangle for less than PLN 100) and there was no problem with the operation.
In case of purchase, the purchased goods can always be returned.
I also ask for a suggestion as to the choice of UPS - the answer to the question.
greetings

Do not any of the honorable Forumers know at least a little about this type of power supplies and can not advise? I would like to close this case at the weekend and I do not know what to choose ...