Just want to be sure: is there ANY difference between sending THB from a US Paypal account to a Thai Paypal account, OR sending USD to the Thai Paypal account and then converting it to THB? Since it's all Paypal, is it all the same?

I have 15USD in my Thai Paypal account that for some reason I wasn't able to convert upon receipt (when I've received in other currencies I get a link asking if I want to convert to THB now). I can't even convert it after the fact, and add it to my THB balance. But to convert and withdraw such a small amount alone requires a 50 baht Paypal fee.

I currently need to send myself some money from my US Paypal account. That's why I'm wondering...can I send it in USD, which hopefully will add to this 15USD already there and I can convert it all at once. And if so, am I getting the same amount I would if I converted it to baht on the US end? I realize with normal banks the answer is "no", but not sure about Paypal.

Depending on the amount I transfer, it may be cheaper through my normal bank w/ 30USD transfer fee instead, just wanted to check this option first.

As long as you set up the receiving account to the selected currency or multi currency then no problem, you can then receive without conversion. The conversion usually happens only when you withdraw into a Thai account, or whatever the bank account currency is.