That shouldn't make a difference, PC3L can run in a PC3 system at 1.5V, PC3 in a PC3L system won't work though it shouldn't fry anything. There is/was AMD only RAM that didn't work in Intel systems but that shouldn't fry anything either.I would guess your RAM upgrade calamity could have been caused by using "PC3L" instead of "PC3" RAM, PC3L is low-voltage 1.35V and PC3 is regular 1.5V.
One thing that I can think of is a power cable getting bumped and unseated causing a short, they have enough power for that and HP systems of the small form factor or mini tower variety can be very cramped on the inside.
A bad non-repair job: the cheap no-name motherboard(probably PcChips) of my first PC shorted out one day so I took it to the place that I bought it from because it was still under warranty, they took a look at it and declared they would do nothing because the little sticker was broken and if a computer had been opened the warranty was void, it said so on the sticker. That's not legal but I didn't know that at the time and I had only opened it to insert a graphics card, months before it died, that was it.
That's when I decided to build a PC for the first time which meant that the individual parts are under their own separate warranty, for personal use system retailers can go fuck themselves.