Yep. Something is definitely shorting.
How long it takes the
fuse to blow could help indicate how severe the problem is. If it's a matter of flipping the
switch and getting a "pop" in response, the
PSU has a dead short, longer infrequent delays before blowing could
point at something more subtle like a faulty component drawing slightly too much more
power than the rated
current.
This is all relying on the
fuse being reasonably within it's
rating and blowing reliably...