1. There is no standard formula to convert VA to watts because several variables come into play, in particular, the "power factor" (PF). But the formula to convert is:
VA x PF = W
If the power factor is not known, the safe rule of thumb is to use 60% or .6.
So in your case, 600 x .6 = 360W. While 360W is not a lot, it is to support your computer, monitor, and your network gear too (as long as the batteries are still good - they typically need to be replaced every 3 - 5 years).
Assuming you are talking about the computer listed in your System Specs, when I plug those values into the eXtreme PSU calculator as seen here
, even with adding a little padding, the recommended UPS is 500VA so you have plenty to give you even a little extra battery run time - a good thing.
It is not uncommon for UPS to make a humming or slight buzzing sound when on batteries. Many UPS also have small fans to keep the DC to AC converters cool and some can be noisy.
2. I am not sure I understand where the shock came from. Unless you power off the UPS with its master power switch, it will output power. You could have also received shock from a static discharge.
However, something could be wrong. You say the main power socket is new - how do you know it was properly wired and more importantly is properly grounded to "Earth" ground? I recommend every home owner and computer user have access to a AC Outlet Tester
to ensure your outlet is properly wired and grounded
. I recommend one with a GFCI (ground fault circuit interrupt) indicator as it can be used to test bathroom and kitchen outlets too. These testers can be found for your type and voltage outlet, foreign or domestic, (like this one
, for example, for the UK) at most home improvement stores. Use it to test all the outlets in the house and if a fault is shown, have it fixed by a qualified electrician.