MBP 13" 2017 w/ Touch Bar - Battery drains while gaming, even though it's plugged in

The day before yesterday I've downloaded the Origin app and installed Sims 4 (base game, pets, seasons + extra user-created content). I've noticed that while playing my battery will drain, even though it's plugged in via original apple-adapter with the power socket (programs active: VLC, Origin, The Sims, finder. Bluetooth is off, WiFi is connected, no other programs are active). The menu bar does indicate that my adapter is plugged in through the battery icon:

I've already done a PRAM & SMC reset, because I've read that this could help with battery issues. It's still happening after. The game itself is on 'normal' display settings (there is a 'high' and 'ultimate' option). These are my Macbook's specs, I thought they were enough to handle such a game:

Is this normal and is the power supply simply not equipped to handle this kind of work? If not, is it fixable though software or is my battery defective? When the origin app and sims app is not active, the battery-level will increase again. I've never had this, even when I've worked with Adobe Photoshop & Adobe Indesign (with several other programs active as well, VLC being one of them) on this laptop a few months ago.

Note: I haven't seen what happens when the battery is drained, I've always closed all programs down when the battery runs too low. I don't know if my MBP can still get enough power through the socket to keep running when the battery's drained.

Thanks in advance.