this is why u would use redundant psu's
pull one out, test it, replace it, pull other out test it replace it be on your way.
technically the server itself comes under the low voltage wiring act (if it has no rails +/-50v). there's a possible, tho prehaps not legal, way round it for you.
the person doing the pat testing should tell you the legislation, or quite clearly there the wrong person for the job and this needs to be highlighted to their manager/as far up as needs go.