use XML::Rules;

my $parser = XML::Rules->new(rules => {}, ident => '  ');

print $parser->toXML(
Shelf_Info => {
    switch => [
        {Name => "Puebla01", shelfType => [7480], commentText => ['ATM
+ Core switch']},
        {Name => "Puebla02", shelfType => [7440], commentText => ['ATM
+ access switch']},
    ]
});
[download]

Not XML::Smart though. It makes use of the fact that the value of a tag attribute may only be a single string, not a hash or array so it's clear that the shelfType and commentText must be a child tag, not an attribute. Generally XML::Rules attempts to create the simplest possible XML that'd contain the data and attribute is considered simpler than child tag.

Update: With version 1.16 I just uploaded to CPAN, it'd be even simpler:

use XML::Rules ToXML => { ident => '   ' };

print ToXML(
Shelf_Info => {
    switch => [
        {Name => "Puebla01", shelfType => [7480], commentText => ['ATM
+ Core switch']},
        {Name => "Puebla02", shelfType => [7440], commentText => ['ATM
+ access switch']},
    ]
});
[download]

You may now instantiate a parser and import a subroutine that'll call the specified method on that instance to simplify the usage.