Nope, I don't have a digital powersupply. Just don't turn it up too much, you don't want that liner needle hitting too hard.
Never used practice skin at all..just really good friends with no money, lol...
I also would suggest doing something small on yourself, on your thigh or something easy to get to. You already have tattoos and know what they feel like, so if you do and it hurts like hell..turn the machine down a bit (I know it sounds funny, but I'm no kidding) You'll be able to see what the line is doing and if you should turn the power up or down, or push harder or lighten up.
I usually hold the machine so it's more up in the air..I can manipulate lines and color/shade better that way,..more range of motion.
"...and my hand starts to cramp after like 10min LOL it sucks.."
I hear ya..try 12 years, I think I've got carpel tunnel syndrome.